From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Photograph of a portable electronic testing apparatus, likely a sound level meter, in its case with a separate microphone unit.
| Identifier | ExFiles\Box 138\1\ scan0219 | |
| Date | 2nd January 1936 guessed | |
| 6. Phon N.S. Reg. Des MS.355.43 | ||