carpenter's rule

17th Century English

Three Fold Ship Carpenter’s Rule -

mast makers rule


The two foot rule, made of boxwood and brass, is in fairly good condition: there is an old repair made with brass rivets. The main division is 24 inches




1. Side A has four scales:

a. An inch scale [0]-18, divided to unit, half, quarter,

eighth and numbered by 1 to 18. This continue to 24 on the brass leg.

b. A pair of  sectoral lines, used for setting out the taper of a ship’s mast.

The inner sector lines on each of the boxwood legs ara graduated P, 3Q, 2Q, 1Q and MH, rapresenting Partners, third, second, and first Quarters, and Masthead. The function of this sector is to provide a series of diameter measurements.

The second, or outer set of the two sector lines are designated S, 3Q, 2Q, 1Q and YA, for Slings, third, second, and first Quarters, and Yardarm.

c. the octagon scale, to left and right of the rule joint, scaled 0 to 28



2. Side B for timber and board measure was designed to be

used for measuring areas and volumes. This particular

format was established during the 17th century as an adaptation

of a design first published by Leonard Digges in 1556

Side B has three elements:

a. The line of board measure running from

9 to 36. The scale ends 4in from the end of the leg (4 x 36 = 144

= 1ft square).

b. The line of timber measure from 11 to


c. A table of timber undermeasure. This is continuous

with the timber line and supplies values for 1 to 8in,

which the rule cannot accommodate on the scale line.


3. The edge carries a logarithmic line of numbers 1-10.

The logarithmic line of numbers on the edge was first

published by Edmund Gunter in the 1620s. In the form

found here, which appeared on a range of instruments in

the 17th century, it would have been used with a pair of



The folding rule is engraved with a monogram CC with fleur de lys and stars (CC may have been the owner, rather than maker)

The feature and the presence of fleur de lys, make it comparable to three-fold rule found at the Colonial Williamsburg collection and probably produced by the same atelier.

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