After I migrated to Avid Media Composer, I spent about 4 weeks happily and unknowingly adding an extra frame to my clips!

It was really by accident that I discovered my error.

Here is an explanation of my error and why it was happening.

After you understand the error, the solution is simple.

Regards,
Douglas

Douglas, that's a pretty good explanation - however, I think one thing you may have omitted is that when you're zoomed in and see the solid line and dotted line.  If you press I and O at the same point you will see the marks surrounding that one frame.  So the In and Out can never be less than 1 frame.  The dotted line is always the Out point. 

Similarly in film, each strip of film is made up of frames.  In your example, you want a a strip of 5 frames, but in order to include that 5th frame you must move to the head of the 6th.

So, the counting of frames is that the In point assumes the head of the frame.  Your Composer window will always display the incoming head frame wherever you are parked.  Marking Out will always assume the tail of the frame.  

Graphically,   |A|B|C|D|E|  (6  In point possibilities, 5 total frames) Notice that if you were to park at the head of B, you're also parked at the tail of A.  But, if you mark In/Out while parked at B, it'll mark surrounding B.  Cutting |B|, would result in |A|C|D|E|  (5 In point possibilities, but only 4 total frames)  

If you don't have a filmstrip that you can look at, you can use a roll of paper towels to understand the logic.

Kenton,

First of all thanks for the extra information.
It gives viewers/readers more things to think about.

Kenton.VanNatten:

however, I think one thing you may have omitted is that when you're zoomed in and see the solid line and dotted line.  If you press I and O at the same point you will see the marks surrounding that one frame.  So the In and Out can never be less than 1 frame.  The dotted line is always the Out point.

Actually I did notice that when I was running through what I wanted to include. I almost included it, but I thought it wasn't necessary.
Too bad you are not a mind reader and could have sent me this before I did the Tutorial

Maybe next time?

Regards,
Douglas