A rare portable aneroid altimeter calibration pressure chamber, R. W. Munro limited, for use by the Air Ministry, London/Harlow circa 1940 The cylindrical brass vessel with screw-clamp end cover secured by turning a large four-spoke wheel, three raised circular glazed viewing apertures flanking internal lamp connection terminals to front and hand pressure pump beneath pipework and valve taps to right hand side, mounted via cast cradle supports onto a rectangular mahogany base applied with brass trade plate engraved REF. 6c/63, PORTABLE CALIBRATOR MK 1, FOR ALTIMETER, R. W. MUNRO LTD, SERIAL No. 263/40, with original conforming box cover applied with repeat trade plate and aluminium plate stamped AM 66 over R & S D and secured via knurled brass screws, (pipework incomplete and lacking pressure gauge), 51cm (20ins) wide. The firm R.W. Munro Limited can trace its origins back to 1783 when James Munro was apprenticed to a mathematical instrument maker in Wapping. His son, also called James, carried on the business, as did two of the younger James' sons. The partnership between the brothers was amicably dissolved in 1864 when Robert W. Munro set up on his own account as an instrument manufacturer, and thereby founded the present company. The firm quickly gained a considerable reputation in the fields of mathematical, optical, meteorological and banking equipment, fields in which it is still prominent. Munro provided instruments for the Scott and Shackleton Antarctic expeditions and, in the 20th century supplied components for the construction of H.P. Babbage's 'Mill', a connection which was renewed in 1956 when the company was commissioned by I.B.M. to construct a copy of the original. R.W. Munro and Co. is perhaps however best known for the development of the Dines anemometer (a design which has remained basically unchanged to the present day) - the demand for which came about in response to the Tay Bridge Disaster in 1879. The company was also involved at an early stage in the production of hydrological and experimental tank equipment, and was a pioneer in the field of aeronautical instruments. The current lot would have almost certainly been supplied to the Air Ministry to facilitate the calibration of aircraft altimeters during WWII.