Len Sumpter's Course & Speed Calculator MKIIA

Len Sumpter's Course & Speed Calculator MKIIA, made by E R Watts & Son, in a fitted wooden case, 28cm. Provenance; with a letter from Len Sumpter offering to sell the Calculator stating, "I have a Course & Speed Calculator (C.S.C) of 1940 vintage, complete with box... obtained for us by G/Capt Cheshire when we did the dive bomb marking in 'Mossies' in '44.". Also another letter from Sumpter stating, "It did go on the 1000 bomber raid on Cologne in May '42 in a Wellington".Len Sumpter's Course & Speed Calculator MKIIA, made by E R Watts & Son, in a fitted wooden case, 28cm. Provenance; with a letter from Len Sumpter offering to sell the Calculator stating, "I have a Course & Speed Calculator (C.S.C) of 1940 vintage, complete with box... obtained for us by G/Capt Cheshire when we did the dive bomb marking in 'Mossies' in '44.". Also another letter from Sumpter stating, "It did go on the 1000 bomber raid on Cologne in May '42 in a Wellington".