Simple question I hope! This is about measuring the boom "black band" -is the measurement from the very back of the mast (sail track) as per equipment rules of sailing definition? I assume it is but I wanted to chack as some classes measure from the back of the mast (ie inside the track).

I believe it is from the back of the track. If the track doesn't continue down to the boom level (like with carbon rigs), then you need to use a flat ruler or something to extend the track to give you a more accurate measurement.

Agree with ross.

Go to the bottom of this page, and see the picture and text below it (in step 15). This defines it as the back of the track.

Tell you what, I'll quote GGGG's words from that article:

"The end of the tape measure has been set at the extension of the sail track, since this is a 'measurement point' as defined in the 'Equipment Rules of Sailing' for the boom band. This is not crucial, but if you were replacing a mast with an integral track with one that has a bonded track the difference could be 20mm."