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T326-26 · Pocket
1939
Object Overview
This Pocket Precision Aneroid Barometer was manufactured in 1939 by the renowned German company R. Fuess, Berlin-Steglitz, one of Europe's leading manufacturers of scientific and meteorological measuring instruments. The barometer is a high-quality, serially produced portable instrument designed for accurate measurement of atmospheric pressure outside permanent observation stations. Despite its compact dimensions — the case measures only approximately 70 mm in diameter — the instrument features a sophisticated mechanical construction, carefully considered design, and the precision workmanship characteristic of Fuess products.
The barometer is accompanied by its original protective leather carrying case, making it convenient to transport and use under field conditions. Instruments of this type were employed in meteorological observations, geodetic and scientific expeditions, and various technical measurements. Their compact size, robust metal construction, and wide measuring range made such barometers suitable for both civilian and military applications.
self-elastic stacked capsule movement
aluminium, brass, copper-beryllium, glass, leather, steel
The barometer is housed in a small cylindrical case manufactured from thin aluminium alloy sheet by deep drawing. This manufacturing technique made it possible to produce a lightweight, sufficiently robust, and virtually seamless shell while minimising material consumption. Unlike the traditional heavy brass cases used for many earlier precision instruments, this barometer employs a lightweight construction particularly well suited to portable measuring equipment.
Under Germany's Four-Year Plan, copper and brass were regarded as scarce materials dependent on imports and were increasingly replaced by domestically produced aluminium. By 1939, Germany had become the world's largest producer of aluminium.
The exterior has a uniform matte finish in a light grey, slightly silvery shade. This is most likely a fine-textured protective enamel, giving the metal its characteristic subdued appearance while protecting it against oxidation and mechanical damage. The coating remains in good condition, although minor signs of natural wear are visible in certain areas.
A small metal suspension ring is mounted at the top of the case in a cylindrical holder.
The rear of the case features a small circular service cover secured by a screw. This provides access to the calibration port, allowing the instrument's readings to be adjusted without completely dismantling the case. This arrangement protects the adjustment mechanism against accidental interference while preserving accessibility for maintenance.
The front of the case is fitted with a thin metal bezel slipped over the cylindrical shell and secured by three small screws positioned around its circumference. The bezel has a slightly projecting, profiled rim and holds a flat, transparent mineral glass crystal, protecting the dial and indicating pointer from dust, contamination, and accidental damage.
The instrument retains its original protective carrying case made of natural light brown leather. The case is precisely fitted to the barometer and has a rigid cylindrical construction with an open upper section, allowing readings to be taken without removing the instrument. A hinged flap protects the dial during transportation and is secured by a leather strap with a metal press stud. An additional internal leather strap holds the barometer securely in position. External leather loops on the sides allow the case to be attached to a belt or another item of equipment. The individual components are joined by neat stitching in light-coloured thread. The leather displays a characteristic age-related patina, minor scuffs, and traces of prolonged use, without compromising the overall preservation of the accessory.
The dial is manufactured from thin aluminium sheet with an anodised surface. Its markings were produced using colouring and stamping techniques, ensuring accurate scale graduation and durable inscriptions. The surface has a light, matte metallic appearance, against which the black graduations and lettering are clearly distinguishable.
A circular barometric scale runs around the outer circumference, graduated in millimetres of mercury over a range of 560 to 790 mmHg. The scale features evenly spaced fine divisions, with longer graduation marks at regular intervals and numerical indications every 10 mm. This wide measuring range allows the instrument to be used not only for ordinary meteorological observations but also under conditions of considerably reduced atmospheric pressure, such as in mountainous regions.
The upper central portion of the dial bears the manufacturer's distinctive emblem, "R. Fuess, Berlin-Steglitz", enclosed within a characteristic geometric frame. Below it, the functional designation "Barometer" appears in large lettering.
Beneath the central pointer spindle is the stamped serial number 1134439, allowing the instrument to be individually identified. Further below is the marking "D.R.P." — Deutsches Reichspatent (German Reich Patent) — indicating the use of a technical design patented in Germany.
The indicating pointer is made of lightweight aluminium and finished with a protective black lacquer coating, forming what is known as a Japanned pointer. It has an exceptionally narrow, elongated profile with a finely tapered indicating tip, allowing precise readings against the small scale divisions while minimising parallax error. The opposite end of the pointer is extended to serve as a counterweight, providing static balance to the indicating system and reducing the influence of gravity on its operation.
The dial is entirely devoid of the decorative elements commonly found on domestic meteorological instruments. Every detail is governed by its functional purpose: the clearly graduated scale, easily distinguishable pointer, manufacturer's markings, and serial number combine to create the restrained, technically precise appearance of a professional measuring instrument.
At the heart of the barometer is a compact, precision aneroid mechanism with temperature compensation, housed within the metal case. Its construction is designed to convert extremely small dimensional changes in the pressure-sensitive element into a sufficiently large angular movement of the indicating pointer.
The sensing element consists of an assembly of two interconnected, self-springing aneroid capsules forming a single pressure-sensitive system. Each capsule is a hermetically sealed, thin-walled metal chamber with corrugated elastic diaphragms, from which the internal air has been evacuated.
As atmospheric pressure increases, the external force acting on the diaphragms becomes greater, causing the aneroid capsules to contract slightly against their own elasticity. When atmospheric pressure decreases, they expand. Although the absolute magnitude of these movements is extremely small, it is sufficient to register changes in pressure thanks to the highly sensitive transmission mechanism.
The material used for the aneroid capsules deserves particular attention. The diaphragms are manufactured from a special high-quality copper alloy — beryllium bronze — possessing excellent elastic properties, high strength, and resistance to repeated cyclic deformation. The use of this material substantially reduces hysteresis and elastic aftereffect, which are characteristic of metallic sensing elements, thereby improving the repeatability and stability of the instrument's readings.
The aneroid capsule assembly is mounted within a rigid framework formed by two shaped metal plates connected by supporting pillars. The plates are manufactured from a lightweight alloy and feature a characteristic finely textured surface finish. This arrangement provides the necessary mechanical rigidity while keeping the overall weight comparatively low.
Movement of the sensing assembly is transmitted to the indicating pointer through a system of levers and gearing. The mechanism incorporates finely manufactured brass components, precision pivots, a toothed sector, and a small pinion mounted on the pointer spindle. Changes in the height of the aneroid capsule assembly produce movement of a transmission lever, which is converted by the gearing into rotation of the pointer across the scale.
The transmission ratio is carefully selected so that small linear movements of the diaphragms produce clearly distinguishable changes in the pointer's position. A fine spiral return spring is employed to eliminate backlash and improve the stability of the readings by maintaining constant engagement between the components of the gear train.
A particularly remarkable feature is the compactness of the mechanical arrangement. Despite the case diameter of only approximately 70 mm, the manufacturer succeeded in accommodating a complete double-aneroid capsule assembly, a lever system, gearing, temperature compensation, and adjustment components. All parts exhibit the meticulous workmanship characteristic of Fuess, while the combination of lightweight aluminium structural components, brass, steel, and beryllium bronze demonstrates a carefully considered approach to material selection.
The Fuess Pocket Precision Aneroid Barometer of 1939 is an interesting example of German precision instrument-making from the late 1930s, a period when long-established expertise in manufacturing highly accurate mechanical measuring instruments was combined with new materials and efficient methods of serial production.
Its most distinctive feature is the combination of genuinely pocket-sized dimensions with a fully developed, highly sensitive aneroid mechanism, a wide measuring range, and a construction adapted for use outside laboratory conditions. The original leather carrying case, precise dating, and good overall preservation further enhance the historical interest of this example.