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).
Test results for Aero Magneto Rotor M.I., comparing Watford and B.T.H. components.
| Identifier | ExFiles\Box 43\4\ Scan087 | |
| Date | 30th September 1927 | |
| X4021 30.9.27. AERO MAGNETO ROTOR M.I. TEST RESULTS. Inclusive M.I. of Watford rotor :- 1.01 lb-inch² B.T.H. " :- 1.48 lb-inch² Rating of spring drive given = 18.6 lb-inches per degree. Natural period of Watford rotor on drive = .00985 sec. B.T.H. " = .0119 sec. Corresponding frequencies Watford = 101.5 ~/sec. 1015 B.T.H. = 84 ~/sec. 840 | ||