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This parameter sets the life-span for all particles given in frames [f]. Just as a memory hook: if you do not know whether a time-depending parameter expects frames or seconds, just have a look at the default value. Frames are always integers, e.g. 5 or 210, while seconds are floats with decimals, for example 4.25 or 6.5.
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To avoid an abrupt disappearance of particles it is recommended to alter the life span and create a more random behaviour. The variation or tolerance is also quoted in frames and [f] and accepts both negative and positive values. Please be careful with very high variation settings, because they can create an unwanted flickering which is noticeable especially with fluid meshes.
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