The measurement of time travel uses the unit San with a symbol of ṩ which measures the rate of change of the flow of time. This measures the change of time in an enclosed bubble of space-time relative to the surrounding change of time outside the bubble. Measured in seconds per second as velocity of the flow of time.
Most commonly it is written as simply a number, which is the number of seconds which pass in real-space for every second passing in null-space. The measurement was developed for use with the Dimensional Fold Drive (DFD) but can be cross applied to any form of time travel to compare scale.
T-Factor
The T-Factor measures the rate at which a vessel within a dimensional fold bubble (or anything really) moves through time based on the DFD field geometry. The resulting measurement is measured in Sans.
For instance, a T-Factor of 1 yields roughly 70.11 seconds passing outside null-space relative to 1 second passing inside null-space. Thus the speed of the time travel is 70.11 Sans.