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Object Overview
This Altimetric barometer in a leather case, dating to around 1980, was manufactured by the Hamburg-based company Gischard and represents a small portable instrument for determining altitude, protected by a zippered leather case.
The body of the instrument is made of plastic but fitted with a chromed knurled bezel holding a slightly convex mineral glass. The bezel carries a linear altitude scale in meters with a range up to 3500. The scale itself is engraved on a silvered brass plate inserted beneath the rotating bezel. The case is additionally equipped with a small chrome-plated suspension ring.
The dial is also made of silvered brass and features a nonlinear concentric barometric scale in millimeters of mercury, ranging from 500 to 780, which is displayed in reverse order so that the values decrease toward the right rather than increase as in conventional barometers.
In altimetric barometers, the relationship between height and pressure is inherently nonlinear: as one ascends, pressure decreases logarithmically rather than uniformly. To ensure altitude readings in meters are convenient and easily interpreted, manufacturers make the altitude scale linear—each division corresponding to the same number of meters. As a result, the barometric scale in millimeters of mercury has to be distorted, becoming nonlinear, with unequal spacing between divisions. The instrument thus “sacrifices” the accuracy of direct pressure readings in favor of a user-friendly altitude scale, where evenly spaced meter markings allow quick and reliable assessment of ascent or descent.
n/a
crank mechanism
beryllium, brass, chrome, glass, plastic, silvered brass
The instrument is designed as an altimeter: its scales are synchronized so that a single movement of the pointer simultaneously indicates the increase in altitude and the decrease in pressure in the same direction, since altitude is inversely proportional to pressure. To avoid duplicating two “opposite” logics, the manufacturer inverted the barometric scale: now both pressure and altitude decrease or increase in the same direction of pointer movement. As the aircraft climbs, pressure falls, and the pointer moves to the right along the linear altitude scale (0 → 3500 m).
A notable feature of this barometer is its compactly arranged movement. At its core lies a self-elastic, sensitive aneroid capsule, probably made of a beryllium alloy, with a folded edge where the corrugated upper and lower membranes are bent and pressed together. The capsule is mounted on a plastic plate. Interestingly, it is the movement of the lower wall of the capsule that is amplified and transferred to the pointer shaft by means of a crank-and-rod mechanism. The pointer shaft gear engages with a toothed rack, the edge of which can be seen in the photographs. Thus, beneath the plastic plate sits the capsule with its main shaft, onto which the movement of the capsule wall is transmitted via a small screw. Above the plate lies the rack-and-gear mechanism, linked across both levels by a small connecting rod that transmits motion to the toothed rack.
In conclusion, this Gischard altimetric barometer combines the practical utility of a travel instrument with a compact and technically elegant movement, exemplifying late 20th-century German precision craftsmanship.