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).
Calculation table for the ampere turns necessary to produce the required flux.
| Identifier | ExFiles\Box 35\4\ scan 038 | |
| Date | 1st July 1921 guessed | |
| AMPERE TURNS NECESSARY TO PRODUCE FLUX REQUIRED. Part. | Matl. | Length (inches) | Virtual section (sq.ins) | Total flux. | Flux density inch units. | Flux density cm. units. | H.{Arthur M. Hanbury - Head Complaints} | A.T. per inch | A.T. Armature teeth. | Lamin: Iron. | .450 | 5 x .095 x 2.5 = 1.185 | 161000 | 136000 | 21100 | 498 | 1000 | 450 Armature core | " | .60 | 2 x .450 x 2.5 = 2.25 | 161000 | 71500 | 11,080 | 7 | 14 | 8 Air gap. | Air | .015 | 1.80 x 2.5 = 4.50 | 161000 | 35800 | 5550 | 5550 | 11200 | 168 Pole core. | Lamin: Iron. | .60 | .85 x 2.5 = 2.12 | 193000 | 91000 | 14100 | 19 | 38 | 23 Yoke. | M.S. | 1.55 | 2 x .25 x 4.0 = 2.0 | 193000 | 96500 | 14950 | 28 | 57 | 89 Total | 738 | ||