Let's say we have maximum CPS set to 16 and let's have a subtitle that has 32 characters.

1) When it is displayed for 2000 ms, CPS number in the main view is 16.0, black and error checking does not complain.

2) When it is displayed for 1994 ms to 1999 ms, CPS number in the main view is 16.0, black and error checking does complain.

3) When it is displayed for 1993 ms and less, CPS number in the main view is 16.0, red and error checking does complain.

Now, case 2) should never happened. I guess that the main view rounds the CPS and only then changes the color to indicate the CPS is too high/low. Error checking probably does not do any rounding. I think the desired outcome would be that error checking would view as too fast subtitles that have CPS => x+ 50ms where x is the maximum CPS. It would be more consistent.

Note that similar problems is likely to effect too low CPS as well.