linguistic:translation
Absolute tube length

For example, given a length of tubing equaling 100 units of length when open, one may obtain the following tuning discrepancies:

Playing notes using valves (notably 1st + 3rd and 1st + 2nd + 3rd) requires compensation to adjust the tuning appropriately, either by the player's lip-and-breath control, via mechanical assistance of some sort, or, in the case of horns, by the position of the stopping hand in the bell. 'T' stands for trigger on a trombone.