A most unusual brass bulkhead mounting aneroid barometer no. 1452 calibrated in bars by Negretti & Zambra, Aylesbury c1950

Aneroid barometer having 7½” silvered and machine engraved dial, the barometric scale calibrated in Bars with a range from 0.880 –  1.050, divided to single units. The upper part marked “Aneroid Barometer” and “Compensated for Temperature,” the lower signed by the maker “Negretti & Zambra, Aylesbury,” and serial no. “1452.” Blued steel pointer, gilt brass index, bevelled low dome plexiglass, lacquered brass bezel.

Conventional Vidie pattern movement driven from a single flux welded 2½” capsule, tensioned on a C spring, the movement with applied corrosion resistant grey paint overall. All contained within low drum form bronze lacquered case, mounting points at 12, 4 and 8 o’clock.

Condition: The subject of a full service, conservation, and calibration under laboratory conditions, see performance chart from dynamic test. The movement working exceptionally well with good sensitivity and progression. The dial with minor marks only, otherwise bright and clean. The plexiglass probably original, appearing professionally formed and fitted though very unusual. The brass case retaining virtually all its original bronzed finish to both interior and exterior.

Comments: This is a very unusual instrument for three reasons: the Aylesbury address has not been noted on barometers until now; normally metric scales are calibrated in millibars – this is the first instrument of its type noted in Bars, and aspects of construction do suggest perhaps a very limited run’ and thirdly, and very importantly the dial is a re-purpose from instruments of a very similar design constructed for mining and almost always showing the supplier as John Davis, Derby – there had been some doubt as to the maker of the Davis instruments, and this conclusively shows that the maker was Negretti & Zambra.

The application for this instrument is unclear. The dial being calibrated in Bars almost certainly defines its use as being in an environment in which Bars was the predominant unit of pressure measurement, in order to avoid confusion when making calculations. This could include mining but might also be related to diving.