A 670 tuning-fork apparatus was displayed at the 1876 Philadelphia Exposition.

Evidence

A Koenig tour de force was displayed at the Philadelphia Exposition of 1876: a “tonometric” apparatus consisting of 670 tuning forks, of different pitches covering four octaves. — Eric J. Heller, Why You Hear What You Hear- An…, 2310

Categorization

• CANDY: Fun fact about a 670-fork tonometer spanning four octaves at a world’s fair.
• XREF: Connects to the instrument-craft thread in this book and to tuning-fork history, e.g. how forks were used as acoustic standards before digital tuners.