Is the Record Playing at the Correct Speed?

Back before MP3’s, CD’s, cassettes, or even 8-tracks, there was an audio storage medium known as a record. Records were played on a “turntable,” as shown above. High fidelity audio required that the rate of revolution of the turntable be carefully calibrated. This was accomplished using a strobe light (shown as a red glow in the photos) and precisely spaced notched rings around the circumference of the turntable.  if the notched ring appeared stationary, then the rotation speed was correct. Multiple rings allowed for callibration at the various speeds. Thirty-three and a third, 45, and 78 RPM were common “formats” for this now antique “storage medium.”

The notched rings provided a simple visual check of proper machine function.