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A half-circle protractor marked in degrees (180°). A protractor is a measuring instrument, typically made of transparent plastic, for measuring angles. Some protractors are simple half-discs or full circles. More advanced protractors, such as the bevel protractor, have one or two swinging arms, which can be used to help measure the angle.
Bisect the line using a compass. Construct a line 90 degrees to the baseline using a compass. Using a protractor, draw a line from either landmark to intersect the 90 degree line off the baseline at the observed angle. This point is the origin of the circle of position. Using a compass again, the entire circle can be drawn.
Animation of construction of a pentagon using a compass and straightedge. 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 straightedge; arguments in these proofs relied only on idealized properties of these instruments and literal construction was regarded as only an ...
A continuously adjustable 0–90° protractor is also in use. An alternative to the T-square is the parallel bar which is permanently attached to the drawing board. It has a set of cables and pulleys to allow it to be positioned anywhere on the drawing surface while still remaining parallel to the bottom of the board.
Dividing engine at the Museo Galileo in Florence.. There has always been a need for accurate measuring instruments. Whether it is a linear device such as a ruler or vernier or a circular device such as a protractor, astrolabe, sextant, theodolite, or setting circles for astronomical telescopes, the desire for ever greater precision has always existed.
These postulates are all based on basic geometry that can be confirmed experimentally with a scale and protractor. Since the postulates build upon the real numbers, the approach is similar to a model-based introduction to Euclidean geometry. Birkhoff's axiomatic system was utilized in the secondary-school textbook by Birkhoff and Beatley. [2]
The protractor head can be used for: Measuring and checking angles between surfaces, edges, and markings. Marking angles from an edge; Directly transferring angles, like a bevel gauge (sliding T gauge), to minimise measurement errors and inaccuracies. Measuring and marking angles relative to the horizontal by using the spirit level. [2]
Breton plotter. A Breton plotter (French: Rapporteur Breton), also known as a Portland course plotter or Weems protractor named after later manufacturers producing similar devices, is a navigational instrument used for nautical navigation with charts.