Saturday, 19 January 2013

The medieval toolchest: compass, calliper and divider

'God took the golden compass circumscribing the universe'. Though this quote comes from 1667, the image fitting this quote very well is from medieval times. The compass is used by architects, masons, navigators, and several woodworking trades. The compass is considered important to the medieval joiner and is often depicted on the guild signs together with the square, the axe and the plane. Compasses are also called dividers.

God as architect of the universe. Bible Moralise, Codex Vindobonensis 2554 (French, ca. 1250), in the Österreichische Nationalbibliothek, Vienna, Austria. The compass has a thin arm fixed to the right leg and sliding through the left leg, providing more stability.

Monk at work as a joiner. Side of a choir stall from the cloister in  Pöhlde, Germany, dated around 1280. Nowadays in the Niedersächsisches Landesmuseum, Hannover, Germany. You can see a selection of woodworking tools depicted including a compass with a sliding arm. Other tools are a square, chisels and gouges, mallet, plane and workbench. Image from

Carpenters are inspected by the grandmaster of the order of St. John in Rhodes. Miniature detail from MS Lat. 6067 by guillaume caoursin, 1480. Bibliothèque Nationale, Paris. On  the ground are several tools including a compass, chisel, square and mallet.
15th century seal of the carpenters guild of St. Truiden, Belgium.

Compasses for coopers are large and made of two wooden legs with iron pins, while compasses for joiners are generally smaller and completely made of metal (iron and/or brass). The legs of a compass are stiffly hinged with a rivet. Compasses are used to scratch circular forms on wood (for instance gothic arches), but also to transfer exact measurements, or to divide lengths in equal parts. Sizes for (excavated) metal compasses are in the range 9-18 cm (Boijmans van Beuningen and 'Ironwork in medieval Britain - an archeological study by I.A. Goodall, ISBN 978-1-907975-455). 

 An iron compass dating from around 1450.

Three medieval compasses made of brass and iron from the collection in museum Boijmans van Beuningen, Rotterdam, the Netherlands . Left:  Compass no. F 6454 (KN&V) dated 1400-1500. Size 13.1 x 3.4 x 0.8 cm. Middle:  Compass no. F 6449 (KN&V) dated 1500-1600. Size  17.6 x 1.5 cm. Right: Compass no. F 6455 (KN&V) dated 1400-1500. Size 9.5 cm.

The compasses of the Thomasguild are antique ones, bought at tool collectors shops.

Our two compasses, made of iron. One has a supporting arm.


Callipers are a special form of compass that occur in two versions, inside and outside callipers. They are used to measure the exact size of a form by placing it between the legs. Outside callipers measure the outside diameter of an item (e.g. the thickness of a stick), while the inside calliper is used to measure the diameter in an item (e.g. the inside of a cup). The callipers are indispensable tools for the turner, used continually to measure the turned item as the work progressed. I have not seen many images of medieval callipers, however a Roman marble relief shows both an incomplete lathe and callipers. An early renaissance book illustration shows many different compasses and a calliper.

Marble relief of a woodworkers shop, originally from an altar perhaps dedicated to Minerva. Tools from left to right are a frame saw, a carpenters square, a calliper, a bucksaw. A lathe may be depicted on the stand in the centre left of the relief and also before the seated figure to the right.  L. 1.38 m, H 58 cm. Capitoline Museum (Montemartini) Rome. late first century. Image from the book Roman Woodworking by R.B. Ulrich, ISBN 978-0-300-10341-0.

Among all the tools at least four compasses and one or two callipers are shown. Title illustration of the book 'Der fuernehbsten notwendigsten der ganzen Archtectur angehorichen Mathematischen und Mechanischen kunst eygentlicher bericht' by Walter H. Rivius, Nuremberg, Germany, 1547.

We use several antique callipers, both inside and outside at the Thomasguild, mainly for our turning work with the pole lathe. All our callipers are made of iron.  

Two outside callipers. The one on the right looks like the one depicted on the Roman marble. 
The one on the left like the one depicted by Rivius in 1547.

 An inside and an outside calliper.


  1. No mention of the twybil (bisaigue or piochon in French, kreuzaxt or stossaxt in German) - a tool that has all but disappeared in the UK, but is still common throughoit most of mainland Europe in one form or another.

  2. How did the dividers without the support arm stay in position? Would one secure it with a wedge and string?