Only Online Auction

Geneva, Apr 07, 2021

LOT 312

A l’espérance
French sector & folding square proportion compass; brass

CHF 400 - 800

EUR 400 - 750 / USD 450 - 900 / HKD 3,400 - 6,700

Proportion compass or French sector, known as a “pied de Roy”, in the shape of a folding ruler, made of brass.
Proportion compass, known as a “demi-pied de Roy”, in the shape of a folding square, made of brass (complete with its two closing pins).

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Grading System
Grade: AA

Very good

Brand A l’espérance, Paris

Year early-18th century

Material brass

Length 225 mm. (unfolding) & 116.4 mm. (folding)

Width 19.2 mm. & 17.9 mm.

Thickness 3.4 mm. & 4.3 mm.

Weight 73 gr. (approx.) & 73 gr. (approx.)

Signature case


Pied de roi
The pied de roi (pied de Roy or king’s foot) is a unit of measurement dating from the Ancien Régime, in use before the creation of the metric system in the revolutionary period (late-18th century). One pied de roi is equivalent to 32.48 cm.
This graduation can be found on various measuring instruments, including one that was given its name: the “proportion compass” or “sector”. It comes in the form of a folding ruler or folding square, and was widely used until the end of the 19th century.
The proportion compass is in fact the ancestor of the slide rule. It was used to make quick conversions or to determine proportions, hence its name, between “homogeneous” quantities, such as lengths, nautical distances, areas, weights, densities, etc. Each type of compass was adapted to one or more specific types of calculation.
These instruments, entirely covered with beautiful engravings, are today real objects of curiosity, jewels to be placed on your desk, which hide innumerable functions.


· Tomash, Erwin, & Williams, Michael, R., “The Sector: its history, scales, and uses”, in IEEE, Annals of the History of Computing, Historical perspectives on computing, software, and networking, vol. 25, January-March 2003, pp. 34-47.


The purchase price payable by a buyer will be the sum of the final bid price plus the buyer’s premium, together with any applicable sales or compensating use tax. In addition to the hammer price, the buyer’s premium is payable as follows: 25% of the hammer price on each lot.

Important notice – Special conditions Please look carefully at all the photos as they are an integral part of the description. Any defect not mentioned in the descriptions but visible on the photos will be considered as described and cannot lead to any claim. The dimensions are given as an indication and may slightly differ from the measures mentioned by the manufacturers especially for contemporary watches. The photos are not retouched. Colors may differ from reality. For timepieces, we guarantee neither the functioning nor the precision of the movement, nor the water-resistance of the case. In addition, please note that movements, parts of mechanisms or cases may be incomplete. The lots are sold “as is”, described to the best of our knowledge and cannot be returned. Once the online bid is placed by the bidder, it cannot be cancelled.