The record groove surface viewed under a microscope. The nearly uniform groove width shows Edison's early square "chisel-cut" recording technique, used prior to August 1889.
National Park Service
Specifications of the tin cylinder phonograph record:
- Estimated original outer diameter (if not misshaped): ~60.4 mm (~2-3/8 inch)
- Estimated original inner diameter (if not misshaped): ~53.7 mm (~2-1/8 inch)
- Width: ~ 11.4 mm (~7/16 inch)
- Thickness: ~ 3.4 mm (~1/8 inch)
- Groove threads per inch: 50
- Groove type: Vertical cut, nearly uniform groove width.
- Recording/playback speed: Unknown. (The playback speed/pitch of the recording as presented here was set by ear.)
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