A
mathematical instrument is a tool or device used in the study or practice of
mathematics. In
geometry, construction of various proofs was done using only a
compass and straight edge; arguments in these proofs relied only on idealized properties of these instruments and literal construction was regarded as only an approximation. In
applied mathematics, mathematical instruments were used for measuring angles and distances, in
astronomy,
navigation,
surveying and in the measurement of time. Instruments such as the
astrolabe, the
quadrant, and others were used to measure and accurately record the relative positions and movements of planets and other celestial objects. The
sextant and other related instruments were essential for navigation at sea. Most instruments are used within the field of
geometry, including the
ruler, dividers,
protractor,
set square, compass,
ellipsograph,
T-square and
opisometer. Others are used in
arithmetic (for example the
abacus,
slide rule and
calculator) or in
algebra (the
integraph). In astronomy, many have said the pyramids (along with Stonehenge) were actually instruments used for tracking the stars over long periods or for the annual planting seasons.