The foot rule consists of a thin narrow strip of metal, hard wood, or ivory, generally 2 ft. long, graduated on both sides into inches and fractions of an inch (halves, 4ths, 8ths, 12ths, 16ths, 32ndths), and hinged so as to fold into a shorter compass for convenience in carrying. Superior kinds are fitted with a sliding brass rule adding another foot to the length, and graduated in minute subdivisions which facilitate calculations of dimensions. In the form shown in Fig. 243, known as "Stanley's No. 32," this brass slide is furnished with an elbow at the end, so that it constitutes a combined rule and calliper (see p. 189). Ordinary prices are 1s. to 5s., according to quality and finish.