Trumpets need a movable tuning slide because fixed third-valve length is inaccurate

Evidence

In practice, on a trumpet, for example, the third valve is often fitted with a tuning slide so that the player can alter the added pipe length while playing. No such issues arise for the trombonist, who can alter the slide position accurately to ensure the appropriate additional pipe lengths are added for accurate tuning of the intervals. — David Howard, Jamie Angus, coustics and Psychoacoustics, 1283

Categorization

• SHARE: Broadly musical rather than very narrow; probably just a general fact rather than one-person-only.
• XREF: connects to: Brass instruments compensate for fixed valve lengths with player-adjustable tuning; Adding valve pipe lengths does not add linearly to frequency drops, forcing compromise tuning; Brass instruments vary pitch by mechanically changing the length of their tubing — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1243 (+1 more)

Broader Connections

• Adding valve pipe lengths does not add linearly to frequency drops, forcing compromise tuning #corroborates (0.85)
• Brass instruments compensate for fixed valve lengths with player-adjustable tuning #expands (0.80)
• Brass instruments vary pitch by mechanically changing the length of their tubing #qualifies (0.75) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1243