millisec test timings and screen refresh rate

[Phil Davis]

I need some help here. My question is basically this: How do I 
accurately track or calculate the exact moment at which an image 
becomes visible on screen?

I have a client whose product is a psychological testing app, with a 
battery of canned tests included. I'm reimplementing it in RunRev, 
moving them away from SuperCard + a large handful of XCMDs. All the 
millisecond timing used to be done in the XCMDs, but now RunRev can do 
it natively, and on all platforms... wait, I don't need to sell you... 
sorry.  ;o)

Some tests require the Rev app to track the millisecs elapsed from 
when an image is displayed on screen to when a user-initiated event 
occurs, like a keypress. This means RR needs to know as precisely as 
possible *when* the image became visible on screen.

(I can already hear some people shifting in their seats, muttering 
"duh! just show the image, unlock screen and put the millisecs into a 
variable!")

Is it that simple? I assume not. I need to figure out when the image 
became visible, not when I told it to become visible. I'll need to 
factor in screen refresh rate, whether testing is displayed on a CRT 
or on a laptop (the normal delivery medium). This also leads me to 
ask: Do laptop screens refresh the same way CRTs refresh? I doubt it.

How have you dealt with this in your RunRev experience? I bet 
*someone* has dealt with this before.

Thanks in advance for all responses. This list is so great!

Phil Davis