[Tom Goldman]

I use a toggle switch bypass to dump the air at the stop . I always warm the trans to 180-200 degrees before checking the rpm. As Keith said set the brake and wack the throttle . I do a 2 second hold . I have a digital dash so it's easy to see the exact rpm . I also data record the test to confirm the rpm .
If you have a properly calibrated carb you should have a nice flat line on the stop rpm .
My test rpm matches my track rpm within 10-15 rpm.