sundial: instrument of many different forms for finding the time from the position of the sun, usually by measuring the position of a shadow, see article on the sundial.
sundial and dividers: a compound instrument combining the functions of both a sundial and dividers.
surveying and gunnery instrument: compound instrument combining functions required in the closely-associated fields of surveying and gunnery, such as measuring bearings and finding ranges.
surveying compass: magnetic compass with fixed sights used for measuring horizontal bearings by magnetic azimuth. See also circumferentor.
surveyor's cross: instrument for establishing right-angled lines of sight, by means either of open sights set at the ends of an equal-arm cross or slits in a cylinder.
surveyor's line: a long string or rope used to measure distances for surveying.