Set of Stanley degree curves at 1/500 scale in a wooden box (c.1900). A mixed (“cannibalised”) set comprising 42 curves (5 missing) from 0′ 30″ to 12′. Most curves are marked “STANLEY LONDON” and “MADE IN ENGLAND”
These curves are similar to a set of railway curves in the collection (eg 1977/009) which have their sizes in inches of radius rather than degrees of curvature. The degree of curvature is defined as the central angle to the ends of an arc or chord of agreed length.
Curvature is more usually measured in radius of curvature. A small circle can be easily laid out by just using radius of curvature. However, if the radius is large as is the case with road and rail construction, the degree of curvature is a more convenient way of calculating and laying out the curve. By this method curve setting can be easily done with the help of a transit instrument or theodolite and a chain of a prescribed length.