Pitch standards varied by four semitones before the tuning fork standardized them

Evidence

Before the tuning fork was used as a frequency standard, pitch could vary by as much as four semitones (two whole notes of the Western musical scale) from one orchestra to the next, or even from one instrument to the next. But even the tuning fork (and the pitchpipe) didn’t prevent the gradual creep upward of concert pitch in Europe, beginning around the seventeenth century. Vocalists tried to rein in this rise, citing strain on their voices. — Eric J. Heller, Why You Hear What You Hear- An…, 282

Categorization

• SEED: Concert pitch creep upward despite standardization tools — an article angle on how technology and taste interact in music history.
• CANDY: Four-semitone pitch variation between orchestras pre-tuning-fork is an easy dinner-party fact.