An extremely unusual and very early purpose built aneroid aircraft altimeter MKI No 17 by Elliott Brothers dated 26 July 1912

Pre-WWI aircraft altimeter having 2¼” dual concentric silvered die struck dial, the crown operated altitude scale calibrated in feet with a range from 0 – 6,000ft and divided to 50ft, the fixed centre marked “Compensated” and signed by the maker “Elliott Bros, London.” Blued two tone steel pointer, bevelled glass

First quality movement driven from a single 1” capsule tensioned on a C spring, all constructed on a circular brass chassis. The whole contained within a semi-barrel form case with twin ribbed decoration, altitude setting crown, calibration port to verso.

Condition: This is a rescue case, found in very original condition, the dial almost unrecognisable, heavily oxidised and badly marked, the movement barely responding to pressure change, the pointer incorrect. A complete rebuild was necessary, the dial cleaned and conserved, the movement repaired using original Elliott parts, the pointer replaced. I’ve taken the unusual step of providing a ‘Before’ image below, for comparison.

Now presenting and working very well across the full pressure range, accuracy as with almost all these early instruments is not so good at higher altitudes or lower pressures.

Comments: This is one of the first dedicated production air altimeters, the product of then arguably the premier maker of such instruments. It is of great historical interest as an artefact of early aviation and as application of the aneroid barometer, restored and conserved to the highest standard with the accent on originality. I have been unable to find a similar instrument anywhere – I have observed both “MKII” and “MKIII” versions of this instrument, the MKII to 6,000ft with a simplified dial pattern and a serial number, the MKIII to 10,000ft with the same dial pattern as the MKII, a serial number, and the movement dated 1915.

This instrument is clearly what would be termed a MKI based on the early date of manufacture, the low altitude at 6,000ft, an absence of any model designation, and the absence of a serial number. Instruments lacking serial numbers where there are others of similar pattern with serial numbers might generally be considered as early production or even prototype. This series of instruments attracted some modifications during the length of their service life and over the MKII and MKIII variants: this particular instrument is, in all respects other than the higher quality, a basic aneroid movement. The MKIII model included a channel set on a short boom mounted on the chassis, positioned axially to the chain which sits within it. Clearly at various points there had been issues with either vibration or possibly lower pressures which had caused the secondary lever to rotate over centre and therefore stick.

Very rare, this is a real collector’s piece.