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).
Graph plotting amplitude in degrees against engine RPM for the Wraith Spring Drive.
| Identifier | ExFiles\Box 124\2\ scan0137 | |
| Date | 2nd April 1940 | |
| B 60 NO 2 WRAITH SPRING DRIVE AMPLITUDE DEGREES .8 .6 .2 ENGINE R.P.M 1000 2000 3000 4000 RM{William Robotham - Chief Engineer} / URS. 2.4.40 | ||