Set square

The set square (actually Geometry Triangle ) is a combination of ruler and protractor in the form of a right-angled isosceles triangle. Today it is primarily a tool for the character and teaching of mathematics that is used there, especially in the sub-region geometry for measuring and drawing angles and makes drawing parallel lines. For technical applications, especially high-quality Geodreiecke are manufactured, which are under the name TZ- triangle ( TZ for Technical Drawing ) in the trade.

Description

Geodreiecke are available with or without a handle on the top, with or without raised dots on the bottom (so-called ink naps ) as well as in different sizes, which are differentiated according to the length of the hypotenuse. This is the longest side of the protractor is also called the ruler edge; she wears a centimeter division with the zero point in the middle. There, the perpendicular drawn to the ruler edge center line that divides the character device in half and the height represents that help can be characterized exactly right angle begins. Lines are incorporated for parallel ruler edge in the triangle. Along the arms of the triangle marks are provided at a distance from an angular degree, the scale runs from 0 ° to 180 ° or 180 ° to 0 °. The angular scale allows the construction of an angle with the accuracy of about half a degree.

Drawn is along the ruler edge. In particular, the right angle at the apex of the short sides of the protractor to draw is unsuitable; so can most the squareness be checked quickly. To draw orthogonal and solders on the other hand you put the center line to the given line and draws along the ruler edge. When drawing from other angles, the procedure accordingly: zero point and angle mark lying on the given leg, the free leg is drawn to the ruler edge.

On some Geodreiecken are next to the right and the inside right angles, the angle 7 ° and 42 ° (or 138 ° and 173 ° ) are particularly marked. This facilitates an axonometric representation according to ISO 5456-3 ( dimetry ).

History

A similar instrument was the set square of the Egyptian surveyors at the beginning of the third millennium BC, used as a so-called construction Remen for field surveys required by the annual Nilschwemmen.

The now common protractor of transparent plastic (PMMA or PVC) was developed in 1964 by the company Aristo.

Variants

A set square with handle and other angular distribution is used in the card set for tasks of navigation and mentioned there Kursdreieck.

Geodreiecke also be used together with a Abschiebedreieck or to a slide rail.