limited clock mode not accurate enough?

i use limited clock mode in Panda and set fps limited at 30. when i read the built-in fps meter of Panda , often i read 29 or 28. 29 is fine, computer always has a little error in calculating float number . but 28 means the program slows down. but i am quite sure it was Panda slept a bit too much , not that my CPU couldn’t catch up.
can the clock limiter be more accurate?
or is the FPS meter not accurate? :unamused: