Events are driven by the currently selected AI storyteller. They range from everyday occurrences like passers by, to all out assaults on the colony.
The player will be notified of an event's occurrence by an envelope icon that will appear down the right side of the screen. Envelopes are color coded according to whether the event is good or bad - blue envelopes denote good events, red envelopes denote bad events, and yellow envelopes denote neutral events.
Clicking an envelope will open up the message with a description of the event, and the option to either dismiss the notification or, where possible, go to the location of the event. Alternatively, notification messages can be dismissed without opening via right click.
These events can take place from Base Builder difficulty onwards.
Commonly known as a raid, this event comes in several types. The size of a raid is determined by your colony's wealth, and the difficulty setting of the AI Storyteller. It is possible for multiple raids to occur at the same time, possibly to the benefit of the player if both raids are from opposing factions.
Different types of raids include:
Assault raids arrive either via the edge of the map or by drop pod. They may assault the colony immediately, or stage for a time before launching their attack, allowing colonists time to take up defensive positions, or to skirmish/counter assault the attackers.
A group of raiders arrives via drop pods directly in the player's base, leaving little time to prepare. Drop pods may punch through a constructed roof or thin rock roof, but not overhead mountains.
Siege raids typically have a party of raiders arrive and set up a small camp along the edge of the map with a number of sandbag walls and mortars which could be explosive or incendiary. They will fire upon colonists, colony structures and any visitors or other raiders from factions they are hostile to, only stopping to eat and sleep.
Siege parties will abandon their camp and any remaining construction to assault the colony when their siege weapons are destroyed or they suffer significant casualties. Any remaining supplies and objects from their camp can be claimed, deconstructed and used by the player.
A bug hive has emerged! It will slowly spawn bugs as well as produce additional hives. If you don't want it to infest the whole area, muster your forces and destroy it. But beware - the bugs will defend their hive.
Infestations will only spawn under an overhead mountain. If all insects are killed, the hives will slowly die out after a while. Hives also bring glow pods that glow for 20 days (as long as they’re installed) and can be reinstalled or sold.
Hives also produce insect Jelly, so if you could trap the hives via walls and doors, you could potentially farm the insect Jelly, though the insects are liable to digging out.
This event can take place from Base Builder difficulty onwards.
A pack of man-hunting animals have entered the area. They will roam the region, hunting for humanoid flesh. If they see a colonist run behind a door, they will attempt to beat down the door. They'll leave the area in a few days.
A manhunter pack has 40% more points allocated to enemy spawning than an ordinary raid (i.e. a manhunter pack is 40% bigger than a standard raid), and animals from manhunter packs will congregate around your base for anywhere from 24 to 54 in-game hours before they all leave. While this is a negative event, it can be turned useful for taming as wounded animals can be healed and tamed afterwards. As well as to butcher meat, killed hostiles are better hauled after the remaining ones fall asleep since they won`t rotten until 2 days have passed, there`s no need to rush for spoils.
- Boars, Wargs or anything that runs faster than a baseline human can be very problematic to deal with even with moderately-well defended colonies because they can easily outrun humans, and they all typically arrive in very large numbers meaning they can easily overwhelm a colony.
- Explosive animals, especially boomalopes, are arguably easier to deal with in larger numbers as chain reactions can easily happen because of their large 3-square blast radius, meaning that even packs excess of 40 boomalopes can trivially be dealt with by half a dozen of people armed with automatic weapons (e.g. Charge Rifles, LMGs, Miniguns etc.)
This event sees a massive piece of an ancient ship crash down to the surface near (or even in) the colony. This ship part happens to contain a hostile AI core that emits a psychic drone that negatively affects the mood of all humans on the map. This drone begins low, but grows progressively stronger the longer the ship part remains, therefore it is advisable to destroy the part as quickly as possible. A colonist's psychic sensitivity traits may worsen or lessen the effect of the drone.
The AI is also capable of emitting concentrated bursts of psychic energy, driving one colonist to an immediate mental break, or a localized blast that drives all animals in the immediate vicinity insane.
Upon attacking the part however, a group of mechanoids will emerge to defend the crashed ship part and its AI core. The size of the group is dependent on colony wealth and storyteller difficulty.
A psychic wave is a pulse of psychic energy that immediately drives a number of the local wildlife insane, causing them to attack the nearest human, and any animal that happens to be standing in their way. A psychic wave is not to be laughed at - most of the wildlife in RimWorld is quite fast, and can close the gap to a colonist before they can get off a second shot, often leading to the colonist being overwhelmed.
Special events only occur during certain circumstances.
This event is related to map generation and may not appear on every map. It may occur more than once per map.
"As (Colonist Name) draws near the ancient wall a sense of foreboding overcomes him. (S)He isn't sure why, but (s)he feels this dusty structure may contain great dangers" -message that appears when the first colonist walks near
A walled out area of the map that can contain either cryptosleep caskets, bugs, mechanoids, treasure, or some combination of those. Open at your own risk by blowing a hole in the wall or deconstructing a section. The cryptosleep caskets usually contain humans, but may be empty. Opening or attacking any casket will cause all the others to open instantly. The people inside the caskets may or may not be dead. If alive, they may or may not be armed and hostile. It's even possible for pawns incapable of Violent to melee attack. If they are not hostile and can walk, they will try to escape. Any alive spacers inside may be captured and recruited, with usually a low recruitment difficulty percentage.
Pod people sometimes come with plasteel, components, and gold. luciferium can be found in these buildings. Ancient structures may include other treasures like psychic lances and pulsers. The caskets can be claimed and used or deconstructed by the colony.
This event occurs during raids randomly, only if relations with other factions are friendly and also during Thrumbo revenge.
When hostiles appear, friendly factions may send fighters on their own will to assist you at no cost, so long as the relations between the friendly faction and the raiders are negative. They won`t assist against their friendly factions. However, keep in mind that friendly fire will damage your relations with the aiding faction and on the other hand, rescuing their downed people will improve relations.
Refugee Chased at (Settlement)
This event will not trigger if the colony doesn't have hostile relations with any faction. Pirate band factions should always be hostile since any attempt to improve relations with them is disregarded by design.
When this event triggers a window appears stating that an individual calls you via radio from nearby, seeking refuge from a faction that is hostile to you and chasing them. The player may choose 'Offer safety' or 'Ignore the message'. Ignoring the message will end the event. Offering safety will spawn the individual as a colonist at the map's edge who proceeds towards the colony. Shortly thereafter, the pursuing faction arrives in the form of a raid entering the map where the refugee appeared. The number of pursuing attackers depends on the current size and strength of the colony.
The new colonist will usually be poorly armed and clothed.
This event can only occur if there is at least one battery with stored power and connected to an active power grid with a power conduit.
At any moment, a power conduit may suffer a fault, causing it to explode and expel all stored power in the attached circuit in the process. The amount of stored power directly affects the size of the explosion, up to a maximum of 15 squares in diameter from a total of 90,000 Wd stored. The explosion can damage any nearby structures, items and colonists, as well as catch anything flammable nearby on fire. The explosion will often completely destroy the one section of power conduit where it occurred, cutting off power to anything past it unless there is another path for the electricity to flow around this damage. Laying redundant pathways throughout your colony prevents this.
In addition to the explosion and fire, it will completely empty all batteries attached to that circuit. Isolated batteries will not be discharged. If this event happens at night and your colony is dependent on solar power, then you may be without power until morning. This could affect your crops growing in greenhouses or hydroponics basins, as well as heaters and coolers.
An animal that was harmed will go mad and target whomever hurt it. The game will notify you if such an animal chosen for Hunting will likely attack if harmed, usually predators. Occasionally, all nearby pack members of that animal's species may start attacking their attacker, possibly killing them.
When this event occurs, a single random animal on the map is driven insane. Like with the psychic wave, the insane animal will charge toward the nearest human, attacking any other animal or obstacle (doors, etc.) in its way. This event is particularly dangerous if a Boomalope or Boomrat turns, as they explode upon death and the latter can also reliably catch up to an unmodified human regardless of traits.
A group of ravenous wood-munching alphabeavers appears at the edge of the map. They will continually eat trees (including any you're farming) and Saguaro cacti until they consume them all, unless you eradicate them first.
It is recommended to bring more than one colonist to exterminate them if you choose to. If one turns manhunter, the whole pack will become manhunters, which can turn individually weak beavers into a small army of killing machines.
Area revealed (red envelope)
A new area has been revealed. It contains ancient, hostile mechanoids. Contrary to its blue envelope counterpart, this one has threat.
You've done something to anger another faction bad enough that they are now Hostile to yours.
This only applies to machines using electricity.
A couple splits, complete with the Mood and Social penalties for both colonists.
Character gains an age-related illness such as a bad back or cataracts.
Due to age or a pre-existing health condition, they can also have a heart attack.
This event destroys most if not all of the colony's planted crops across the map, including hydroponic crops grown indoors. Be sure to keep a reserve of food to counter the issue or resort to hunting until more food can be grown.
Devilstrand mushrooms are immune to this event. Any trees in your growing zones that are native to the biome are spared, but not other trees you may be growing.
Bonded animal's death
An animal with bond to a colonist dies, affecting mood negatively.
This isn't a random event on its own, instead being a possible consequence to them. It can occur by slaughtering, euthanizing or intentionally attacking the animal. Wild predators may hunt and kill your animals, including bonded ones. Enemies may target your animals during attacks or even hit them unintentionally while shooting at your colonists. Bonded animals can also fall into traps.
Bonded master's death
The exact reverse of a bonded animal's death. This time, it's the master who dies, through causes such as enemy raids or disease.
When this happens, any animal that is bonded to the master will have a mental break. It can be a less dangerous one such as a dazed wander, or a more dangerous one such as a berserk rage.
Caravan Ambushed / (manhunters)
While travelling, one of your caravans will be attacked. The game will give you a mini map to defend it.
The attackers can be an enemy faction lying in ambush or a rampaging manhunter pack your caravan unfortunately trespasses upon.
A cold snap makes the temperature of a colony drop for several days. Colonists will complain about the cold, especially sleeping in it if their rooms are not properly heated.
While this is generally good for item preservation, it can kill off crops, influence colonist moods and cause Hypothermia if colonists or animals stay in non-heated areas for a prolonged time. It also renders most of the plants in the area inedible (unless when it happens in warmer areas in which some plants are still edible), potentially causing tame animals to starve to death and wild ones to leave the map. With no other food, predators may attack colonists and tame animals. Snowing may also happen, depositing thick snow that can slow down outdoor movement significantly.
Pirates approach your caravan and demand that you give them items and hand over members as slaves. If you don't they will proceed to assault the caravan.
You can see the number of pirates when they are demanding you hand over items.
Several of your colonists and/or prisoners will be afflicted with a disease. The chance, frequency of which disease they are infected with depends on the biome, and the number depends on the disease and the cruelty of the storyteller. Only humanlikes can catch infectious diseases.
Non-blunt trauma wounds, treated or not, also have a chance to get infected. The chance depends on treatment quality and environment. Animals can also catch infections at a greatly reduced rate.
During a solar eclipse, solar generators cease producing power, and outdoor crops stop growing. Be sure to have power and food stored for times like these, or an eclipse coupled with a raid could be the death of an unprepared colony.
A localized, intense lightning storm in one area of the map. Causes big fires. Clicking the envelope icon offers the option to jump to the location where the strikes will be.
A character or tamed animal suffers a heart attack. Characters will go to rest to any bed assigned to Medical instead of returning to his or her own assigned bed and animals will return to the nearest empty animal bed or sleeping spot. Doctors will then proceed to attempt to resuscitate the victim, using medicine up to their assigned medicine level if available.
During a heart attack, people or animals can fall unconscious or even die if not treated in time.
A heat wave sweeps the colony, driving temperature up for several days. Colonists will complain about the heat, especially sleeping in it if their rooms are not properly cooled. Additionally, things might rot in inadequately cooled freezers. There is also a chance for a fire to randomly appear on the map which can quickly spread and burn down an entire colony.
Heat waves sometimes can be deadly to unprepared colonies, mostly tribal ones since they have it harder to build air conditioners since they start without that technology and it takes longer to unlock it. For them it's advised to use passive coolers in rooms or food stockpiles to prevent food from rotting quickly and colonists and animals from getting a heatstroke. Dusters and cowboy hats provide heat insulation for colonists, protecting them while they're awake, though they don't affect mood caused by sleeping in hot areas.
Additionally some animals will leave the map if the temperature gets higher than they can stand.
Mental break: (Type)
One of your colonists has had it and has a mental break. During this time, they will be unavailable for colony work and may possibly cause more trouble for themselves or others, depending on the type of break.
One of your colonists or animals has taken too many drugs in a short amount of time and potentially permanent damage or death could occur.
A Poison Ship event kills plants in an expanding circle, eventually reaching the entire map. Do not confuse this with the plant killing snow aura present on both Poison Ships and Ancient Crashed Ships. The poison kill crops randomly, including plants grown in Hydroponics basins. The affected areas will ultimately have dramatically reduced chances of maturing simple crops, and slower crops will end up nearly impossible to grow.
Prisoners have staged a breakout! They have somehow defeated the door lock and are making their way out. They may seek weapons, fight, or try to escape. Prisoners are more likely to attempt breakout when they are unhappy, numerous, and healthy.
Drone in this case does not refer to "Unmanned Aerial Vehicle" but instead "To produce a low-pitched hum or buzz."
A Psychic Drone phenomenon affects all colonists of a randomly chosen gender, negatively influencing their mood. Colonists have no choice but to endure it as the point of origin is off map. Psychic sensitivity traits can be a big factor in the threat posed by this event. There`s also a positive version called Psychic soothe.
All roofs must be supported by a wall or rock within 6 spaces with roof sections in between itself and that wall or rock. If either of these conditions changes, then the roof will collapse.
If nothing is crushed by the roof then a simple notification will trigger. If something (be it an item or a colonist) was hit then they will take damage and an alert will trigger.
If demolishing a building, it's recommended to use the Expand No Roof Area tool to remove the roof first before deconstructing the walls.
Solar flares cause all electrical items on the map to stop working for the duration of the event. Solar flares are particularly dangerous for colonies that rely on turrets for defense, as they will be vulnerable to any raid that arrives during the solar flare.
During the summer, they will cause coolers to fail, causing any frozen perishable goods to begin spoiling; in cold areas, heaters will fail causing ground based greenhouse crops to quickly die as well, this can be abated with campfires though. Colonists will also be at risk of getting heatstroke or hypothermia if you're in an area with extreme temperatures and don't have other temperature control devices.
Crops grown in hydroponic basins will rapidly die regardless of the temperature. It's recommended to quickly Harvest any crops that can't be saved before they die.
A distant chemical fire has released a plume of poison over this entire region. Any person or creature not under a roof will be slowly sickened by the toxic dust settling out of the atmosphere. It will last for anywhere between a few days to over a month.
Plants will wither under the fallout. This event will usually wipe out all wild animals and poses a serious danger to tamed ones unless they are restricted to an area under a roof. Toxic Buildup, which is caused by toxic fallout, can cause dementia, and eventually a carcinoma (according to game files) if it progresses far enough. However, the latter is treatable via a lengthy operation with the use of at least Medicine, or removed via a surgery.
If you are running low on food, wait for animals to die and then butcher their corpses.
A distant supervolcano has erupted and begun spewing millions of cubic kilometers of ash into the atmosphere. Ash in the atmosphere will obscure the sun. Temperatures will drop, plants will suffer for lack of sunlight and solar panels will not produce as much power. It could pass in a few weeks, or it might last many months.
Volcanic Winters also appear to significantly reduce the inflow of wildlife (observed in a Temperate Forest, 300x300, very few animals came in from Spring-Summer when there'd normally be many), which can easily lead to meat shortages and famine if you don't have sufficiently large farms for your colony.
A grove of the mysterious ambrosia bush has sprouted nearby! If you wait for the plants to grow, you'll be able to harvest the delicious, pleasurable, and slightly addictive fruit.
Tamed dogs or farm animals join your colony.
A random animal on the map becomes self tamed.
Previously tamed animals which return to the colony can self-tame. When doing so they retain all training they previously had.
Area revealed (blue envelope)
A hidden area has been opened up on the map. It's often associated with deconstructing a wall section of an Ancient Danger, which are usually easy to find due to their rectangular shape.
It can also occur with mining, sometimes by accident, but sometimes entrances to these areas can be seen on the map. Look along the edges of a mountain for one or more visible edge blocks facing inward. Mining this section out can reveal new mineral riches, new farmland, new animals, new threats... or absolutely nothing.
Bandit camp opportunity
Some ruffians are causing trouble nearby and other factions will pay you to wipe them out.
Other friendly factions may make a special trade request of you. The popup will specify which goods they want and the price they're willing to pay for them.
From time to time, cargo pods from the wreckage of the ship will fall out of orbit and land on your map. Each drop will contain only one type of resource in a random amount. The remains of the pods become pieces of slag, which can be refined into usable metal at an electric smelter. The pods have a chance of crashing through the roofs of any buildings, damaging any nearby furniture and structures.
Rarely, an escape pod will crash land nearby. The occupant will be incapacitated, but can be rescued and treated or be captured and possibly recruited into the colony. It's possible for the person to be related to someone in the colony. This is indicated on the notice as Escape pod (relationship). Usually, this pawn will join the colony once healed. Still, the pawn has the opportunity to walk off on their own once healed. If you do nothing, they have the same opportunity to stand on their own after awhile and walk off, depending on their injuries.
For a near-guaranteed way to recruit them, capture rather than rescue them. Their recruitment difficulty percentage is usually low and this will also train your warden's Social skill.
Later in-game, friendly AI will contact the colony and reveal the location of a working ship that the colonists can use to escape this Rimworld. The ship is located in a map tile that is always far away, usually requiring several stops along the way to resupply.
This event occurs only once.
This notification will appear once relations have been improved with a Hostile faction enough that they will no longer be hostile. Common ways to improve relations include releasing prisoners from their faction or gifting silver via the comms console. Note that released prisoners must leave the map safely to receive the bonus.
Item Stash Opportunity (Time Remaining)
Another faction leader will offer to tell you for a price the location of a cache of items nearby on the map. The items will often be guarded and others will gather the items first if you aren't fast enough getting to them.
Note that you must have enough silver near an orbital trade beacon to pay the price. Oddly enough, you can receive this message from the other factions without building a comms console.
It is possible that the stash generates with an initially hostile faction guarding it, but that the faction later turns friendly. If so, the guarding members will spawn as friendly and will not attack your faction members.
Marriage is on!
A couple that has been together for awhile will announce their engagement. The wedding will take place some time in the future. This allows players to have enough preparation time to build a Marriage spot if they choose. If not, any Gather Spot will do. When the day of the wedding arrives, it will take place regardless of the entire colony's attendance.
Colonists who do not reach the meeting point on time, such as those sleeping, fighting fires or lying incapacitated in bed, will not gain the mood buffs. A quick Draft and Undraft should be enough to distract all capable colonists to attend. Colonists in caravans cannot attend.
If the couple happens to be busy at the exact moment the wedding is to take place, for example, because they are loading a caravan, those who are not members of the trade group will remain waiting at attendance and perform no task at all except for eating until the couple comes back. This can cause characters to get binges and no wardens or doctors looking out for prisoners can easily let captives break out.
Two characters fall in love. Build them a 2 pawn bed and assign it so they can sleep together. This avoids a mood debuff for both colonists and occasionally gain them another buff.
You'll get this notification whenever a Warden has succeeded in recruiting a prisoner.
One of your colonists will throw a party, improving the moods of all attendees for some time and providing an opportunity for rapid Social changes. They will usually have beers and smokeleaf joints if available. Note that the player may have to wake up any sleeping colonists such as Night Owls or otherwise distract other colonists from their work so that they attend the party. An easy way to do this is by quickly drafting and undrafting them.
Colonists will continually get stacking mood buffs while enjoying themselves at a party. Each stack adds +1 to mood, lasts 10 days and stacks up to 15 times.
The party by default will happen around an item checked as a Gather Spot such as a table, but may be overridden by building a party spot.
Similar to marriage ceremonies, characters that do not reach the party on time don't get the mood buffs.
Precious minerals found
Once the long-range mineral scanner is built, an event similar to a treasure stash can occur on average once every 30 days.
When the player reaches the spot, a temporary map will be generated with a precious mineral lump in the middle.
The minerals may be surrounded by pirates guarding the reserves or a manhunter pack.
When this event triggers it gives a positive mood modifier (+15) to all colonists of a randomly chosen sex. The event lasts between 1.5 to 3.5 days. It can be considered the opposite of the Psychic Drone.
Traders from other non-hostile factions can stop by your colony, whether specifically requested via the comms console or randomly on their own.
Trade Ship In Range
When an orbital trade ship passes near the colony, players may spend silver to obtain resources or weapons, or alternately sell excess resources or weapons for silver. You will only receive this notification if you have built a comms console and it's powered.
You need to build orbital trade beacons so you can beam items up to the ship to actually carry out transactions. You can still check the items for sale even without them however.
Pirate Merchant In Range
Slave traders are rarer than regular traders. They traffic in that most precious of cargo: fresh colonists. Players can also sell unwanted prisoners to slave traders, however any colonists without the psychopath trait will suffer a mood penalty for doing so and the colonist doing the selling will receive a social penalty. As with regular trade ships, you will only receive this notification if you have built a comms console and it's powered.
Wanderer joins / (relationship)
A random colonist arrives from a map edge and joins the colony immediately. They will most likely be naked, so have some spare clothes ready just in case. Notification: A villager named (name) has arrived and is joining the colony. (Gender) is a (backstory).
Somebody who is already married starts an affair with a single person.
This notification will appear when a caravan has arrived at a settlement chosen for attacking.
Once you've designated a caravan, you'll get this notification once all of the colonists, prisoners, animals and items have been assembled and left the map. It is now ready to send to other settlements or form another settlement of your own, if you've enabled multiple settlements in the game's settings.
Leader Replaced: (Faction)
Occasionally, the leader of another faction will die or be replaced. The popup window will announce his or her successor.
This will also happen if the leader comes to raid your base, and is either killed in action or captured and recruited.
One or more thrumbos will spawn at the edge of the map, staying around for awhile to eat anything they can, including your crops. The player can attempt to hunt or tame them, both of which are very difficult. If no action is taken, they will leave on their own after a few days.
Occasionally, one or more members of a friendly faction will arrive, just passing through. They'll enter at one edge of the map and proceed across the map. They'll exit the map upon reaching another edge.
A drafted colonist can be directed to capture (arrest) one of the travelers, however that entire faction will immediately turn hostile.
This isn't an event on its own, but rather an addition to other events that involve other pawns. In any event with other factions, there is a chance that one or a few of the visitors or raiders may be related to existing colonists.
Friendly faction members may stop by your settlement. Occasionally, they will have a few goods to trade. Like a regular trader they will mill about the player's colony for awhile. Unlike a regular trader, they don't have many goods with them, nor do they have as much silver to buy your goods.
Visitors possess no higher purpose otherwise. Still, their arrival could prove advantageous if the colony is assaulted by a mutual enemy while they are present.
Sometimes there will be a singular visitor. In this case, the game will notify you of the backstory of that visitor.
|Category||Name||Common Name||Chance||Favorability|| Min Time Before|
|Disease||Flu||Flu||varies by biome||Bad||varies by biome|
|Disease||Plague||Plague||varies by biome||Bad||varies by biome|
|Disease||Malaria||Malaria||varies by biome||Bad||varies by biome|
|Disease||SleepingSickness||Sleeping Sickness||varies by biome||Bad||varies by biome|
|Big Threat||AnimalInsanity||Mad Animals!: (Animal name)||1.0||VeryBad||1|
|Big Threat||ShipPartCrash||Psychic Ship||1.5||Bad||30|
|Big Threat||ManhunterPack||Manhunter Pack||2.0||Bad||15|
|Small Threat||AnimalInsanitySingle||Mad Animal||5||Bad||3|
|Small Threat||ColdSnap||Cold Snap||3||Bad||30|
|Small Threat||HeatWave||Heat Wave||3||Bad||30|
|General Bad||SolarFlare||Solar Flare||1.5||Bad||30|
|General Bad||PsychicDrone||Psychic Drone||1||Bad||30|
|General Bad||ToxicFallout||Toxic Fallout||0.25||Bad||180|
|General Bad||VolcanicWinter||Volcanic Winter||0.11||Bad||280|
|General Good||TraderArrivalGeneral||(Trader type)||13||Good||0|
|General Good||TraderArrivalSlaver||Pirate Merchant||4.5||Good||0|
|General Good||WandererJoin||Wanderer Join||0.4||VeryGood||0|
|General Good||ResourcePodCrash||Cargo Pods||6.0||Good||0|
|General Good||RefugeePodCrash||Escape Pod||1.5||Good||0|
|General Good||PsychicSoothe||Psychic Soothe||1.0||Good||30|
|Biome Name||Flu||Plague||Malaria|| Sleeping
|Biome Name|| Mean Time