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).
Strip chart recording from a test, showing a value decreasing over time.
| Identifier | ExFiles\Box 38\5\ Scan052 | |
| Date | 2nd March 1919 | |
| 2nd section of test Record of PDL9 ; on 383 Circuit; Date 2/3/19 = 66.6 a.h. | ||