I?m using FCP to edit a short film and my sound editor is using ProTools to sound edit the film. After I?ve added or subtracted a shot or two from a sequence, I need to calculate the difference in frames so my sound editor can conform the audio to the changes in picture (in ProTools).

I?m trying to figure out the formula I should use when I calculate the difference in frames.

a) Should I calcuate using ?non-drop frame? (1 second = 29.97 frames and multiply the number of seconds x 29.97)?
OR
b) Should I use the ? drop frame? formula (1 second = 30 frames, but subtract 1 frame every minute. Except for the 10th minute)?

I get differrent results when I use these different formulas. Which will provide the best, most accurate result for my sound editor?

DF vs NDF is perhaps one of the most confusing concepts to grasp.

First of all, the frame rate in NTSC is the exact same whether you're using DF or NDF. NTSC Video plays at one speed only and that's 29.97 fps. When SMPTE developed TC, at first it was only available in NDF... assigning one unique number to each frame. Broadcasters quickly realized that their one hour shows where timing out to one hour and a couple of minutes more according to this new ndf timecode. This is because at a speed of 29.97 (not 30fps), every second was accumulating .03 frames "extra" time. The solution to this problem was to keep the speed the same and simply "DROP" a frame designation every minute. NOTE: no "frames" are dropped, only a number in the sequence. This ensures that the SMPTE frame number corresponds with a real clock. Now broadcasters could match SMPTE to the clock and every show would end exactly on time.

So, to answer your question.... a frame is a frame. If you remove five frames, your protools guy must remove five frames. There is no difference. To avoid confusion, he should be using the same timecode flavor as you did.

Mark