The medieval toolchest: the rule

Rules are found with woodworkers, architects and stone-masons. A rule is used for measuring, drawing straight lines and checking if (planed) surfaces are flat. They were made from seasoned hardwood as they need to be straight without any flexibility. W.L. Goodman states in his book 'The history of woodworking tools' that the seasoned oak came from barrels or casks bought for this purpose. This is remarkable as staves from barrels are not straight.

 A rule from the engraving 'Melancholica' of Albrecht Durer, 1514. The rule has two holes at the end.

 A similar rule at the bottom of this engraving of a carver making a wooden statue. 

Wood engraving from Nurnberg, around 1550.

 Two carpenters at work to build the cross. The right man uses a rule. 
Jean Fouquet, around 1450. The Hours of Etienne Chevalier, F 76.

The rule is also the sign of authority for the master craftsman (carpenter, joiner or architect), and its use became a guild privilege for the master craftsman in the 16th century. 

Tombstone of the architect Hughes Libergier, 1264. Reims cathedral, France. 

The rule shows several divisions.

Church building. The architect holds a rule in his hand. 

Miniature from La Legende de St. Denis, 14th century. Paris Bibl. Nat. Fr. 2092, fol.75 v.

Rules were divided into equal parts by lines across the width; (some) parts could also be subdivided into smaller units. A certain number of parts could be marked with a circle inscribed over the line. There is no consistency to be found on images on the size or how many divisions a rule had. Divisions were likely feet, inches (thumb width) and arms length (voet, duim and el in Dutch), but it is known that each region more or less had its own inch/feet/arms length. However, for a joiner the exact size of a feet or inch hardly matters. He will use his own measurement tool in his workshop. As long as all his rules have similar markings and the divisions are identical, he can make what he wants. (The Egyptian rule, where each unit is subdivided differently into e.g. 2, 3, 4, 5 and up to 10 parts might also have been very useful to the medieval woodworker).

Two of our oak rules. One is one foot long, the other 2.5 feet.

Our rules are made from seasoned oak and immersed in linseed oil. As the size of the divisions on the rule are arbitrary, we have used the thumb width of the master joiner of the Thomasguild, which is around 27 mm. Twelve inches make up one feet (~325 mm). The long rule is two-and-a-half feet long, the short rule one foot. For the long rule I used circle markings for each half foot, and subdivided the inches of the first half foot in two units. The short rule uses half inches subdivided into two units. Both rules have markings on two sides for ease of measuring.

Detail of our oak rules. Note that the markings are on two sides of the rule. 
The circle markings indicate half a foot.