Groovy
In my useless H.S. notes (prior to my university degrees, lol);
Grooves: It shall be standard that the grove shape for a finished monophonic discs shall have an included angle of 90+/-5 degrees, a top width of not less than0.0022 inch, and a bottom radius of not less than 0.00025 inch. It is recommended that the discs with these groove shape characteristics be reproduced with a stylus having a tip radius of 0.001 inch (+0.0001 inch, -0.0002 inch) and an included angle 0f 40-55 degrees.
It shall be standard that the groove shape for finished stereophonic discs shall have an included angle of 90+/-2 degrees, a top width of not less than0.001 inch, and a bottom radius of not greater0.0002 inch. It is recommended that discs with these grove shape characteristics be reproduced with a stylus having a tip radius of 0.0005 to0.0007 inch and an included angle of 40-55 degrees. In stereophonic recording both channels are recorded i a single grove.
FCC Rules and Regulations, Part 73, Subpart F; 1964.
P. J. Grey, "Disc Recording and Reproduction," American Photographic Book Publishing Company, New York, New York; March 1964.
"Reference Data for Radio Engineers", fifth editions; Howard W. Sams & Co., a subsidiary of Intenational Telephone and Telegraph Corporation, 1968.
by, Federal Telephone and Radio Corporation, 1943, 1946, 1949.