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).
The stroboscopic method of speed measurement with related formulas and a data table.
| Identifier | ExFiles\Box 79\1\ scan0253 | |
| Date | 1st April 1937 | |
| X. 2720 STROBOSCOPIC METHOD OF SPEED MEASUREMENT+ Frequency of supply = f No. of views per second = 2f " " " " minute = 120f. Regular figure of s sides running at speed N R.P.M. recurs. sN{Mr Sanderson}/n times per minute. where n is an integer i.e. 1, 2, 3, etc. If sN{Mr Sanderson}/n = 120f. N = 120 fn / s If f = 40, N = 4800 n / s TABLE: s/n | n=1 | n=2 | n=3 | n=4 | n=5 --- | --- | --- | --- | --- | --- 3 | 1600| 3200| 4800| 6400| 8000 4 | 1200| 2400| 3600| 4800| 6000 5 | 950 | 1920| 2880| 3840| 4800 6 | 800 | 1600| 2400| 3200| 4000 7 | 686 | 1371| 2057| 2743| 3429 8 | 600 | 1200| 1800| 2400| 3000 ETC. | ||