Timecode math

So this odd thing happened on my timeline the other day...

I add together two segments of an hour long show, each one is 7-9 minutes long and I'm at about the 25 minute mark of the show. The timecode starts at hour 1. The end point of clip 1 ends with :17 frames, the length of clip 2 ends with :18 frames. So you would think when adding those together your new endpoint would end at +1:05, right? But it went to +1:03, dropping two frames.

I know about thedrop frame increments, although I don't have it committed to heart. But this was the first time I had noticed any funny math within FCP. I had never seen this discrepancy betwen clip length and the timeline before, and the producers with me were freaking out and re-adding everything, because the show had to come in at a set length. In the end a few frames missing didn't matter much. Still, if one had to ensure total accuracy would they edit non-drop frame?

No...for complete accuracy you would edit Drop frame. Because video runs lightly slower than 30fps...29.97 fps to be exact. So to ensure proper timing, 2 frames every minute, except every 10th minute, is dropped.

To ensure proper accuracy, use either a timecode calculator (VERY handy) or mark IN and OUT and see what the duration is. Just adding in your head means that YOU might not take into account the dropped frames...