Concert · B♭ · C. Read the same music in any key, and hear it on either horn.
the melody (concert pitch)
8 notes parsed.
What a B♭ trumpeter reads. Written a major 2nd above concert.
Written up a major 2nd from concert, so concert C' appears as D' on the B♭ trumpeter's page — but it still sounds C'.
This is the everyday puzzle of the trumpet: a B♭ horn reads a major 2nd higher than it sounds, a C horn reads at concert. Drop in any concert line and see — and hear — exactly what to read on each instrument.