valve 1 adds 0.12246+valve 3 adds 0.18921
so you get ×1.31167
but you need ×1.33484 (that's 2^(5/12))
the note comes out 30.3 cents sharp
watch for this
Lengths add, pitches multiply. Valves 1 + 3 land 30.3 cents sharp.
Adding two pipes adds their lengths. Dropping five semitones multiplies the length by 2^(5/12). Addition and multiplication are not the same move, so the note lands short — and every trumpeter in the world corrects it by hand, on a slide, several times a minute.
The full lesson behind this: The trumpet →