Rockwell Hardness testers by Reicherter (Georg Reicherter) Briro Automat Rockwell Hardness Tester. Instruction Book (in English and German).

Rockwell 6-inch Jointer Illustrated Parts Manual Model 6520-1.

Rockwell Hardness Testers Models JR and J5. Operators Instruction Book.

Rockwell Hardness Testers by the original US Wilson Company (then Acco Industries). Not a manual but a detailed explanatory Booklet from the 1980s describing how to determine which type of tester to choose for different jobs and materials with copious notes on the different types and methods to be used.

Rockwell Hardness Testing Methods (Engineering Series): Explanatory Booklet.