1. the first object i display gives me an onset delay of 16-17ms which is not a problem but i wonder why its not a multiple of the refresh rate

2. does prerelease need to be sync'ed with refresh rates? second object i display (with prerelease set for the first object) gives me an onset delay of 7-8 ms which never changes, no matter what prerelease values i use for that object. and then this delay 'transfers' to the third object in the display and again, whatever values i put, the onset delay for this third object doesnt change. i know how to calculate prerelease values (as noted in one of the other posts) so what could be an explanation of this?

THANK YOU!