Speed reckoner of lime wood designed by Captain McClean and made by C.T. Cooper & Sons. With this reckoner it is easy to convert an observed distance per unit of time in miles, into speed per hour.
Rare specimen in excellent condition.

Catalog: NM.4-19
Date: 1919
WL: 5,7×64,5 cm (2.2×25.3 in)
Signed: Capt. W.N. McClean A.M.I.C.E. July 30th 1919
Origin: England
Condition: perfect