New to Version 10 – a straight forward manner of handling the time parameter
Time is collected in FCS data as an offset parameter – the amount of time steps that have passed since the last collected event is recorded. The $TIMESTEP keyword can then be used to decode the actual amount of time that passed between events. The issue with this means of handling time has been that now all cytometers use the same unit for the time step, and that this isn’t annotated within the data at all. This can lead to data that just doesn’t match the $BTIM (beginning time of collection) and $ETIM (ending time of collection) range.
We now use $ETIM – $BTIM to calculate the amount of time that acquisition took, and then interpolate to map this range to the offset Time parameter. If those two keywords were not collected, and this is rare, a user can add them via the keyword tools and enter the the beginning and ending collections times. FlowJo can then make the calculation based on these entered values.
If no $BTIM or $ETIM values are present FlowJo will substitute event number for a time parameter when needed, such as for the kinetics platform.