1. This rule has a slightly unusual complement of scales in that it has an A scale but no B scale.
2. The cursor has hairlines enabling the rapid calculation of the area of a circle given its diameter.
3. The principal scales on the front have short extensions beyond the usual limits (e.g. the C scale goes to 0. 94 rather than 1.0). On the back of the slide the sin scale extends to 5° rather than the more usual 5° 44'. However the extension of the C scale is not quite long enough for the value of sin  5° to be read.