Sure, but the start and end value are the easiest ones to measure. As I alluded ...

ehsankia on Oct 17, 2017 | parent | context | favorite | on: Keyboard latency

Sure, but the start and end value are the easiest ones to measure. As I alluded to, once you have the two extremes, you can the activation plot [1] to get the exact activation time. For the case of Cherry MX Blue, it would be at 62.5% between the start and end.

[1] https://i.stack.imgur.com/GzswL.png