A one-foot rule is formed from two arms, but has three other pivoted arms and a plumb-bob so as to be configured as a square, level or clinometer, with all the components folding away into the folding rule.
The rule , with a central hinge , has two linear scales running across both arms, 1 to 12, divided to 1, numbered by 1, and 1 to 96, divided to 4, subdivided to 2 and to 1, numbered by 4. Divisions are alternately hatched and mirror finished.
The arm for the square is pivoted close to the hinge. The jointed arm for the level is pivotet at one end of the rule, while the other arm has a hole for location on the pivot pin of the square arm. The brass plumb-bob is shaped and pierced and has foliate decoration. There is a small pivoted clip for securing the plumb-line when stowed.
One arm of the rule also has two clinometer scales. An inner scale is 20 to 0 to 20, divided to 5, subdivided to 1, numbered by 5 with alternate hatching, and is marked 'PERPENDICVLVM'. The outer is  to 0 to , divided to 5, subdivided to 1, numbered by 5 with alternate hatching, and marked 'ALPHARIVM'.