An apparatus for geometrical studies comprising a casing 1 with a front and a back. The front has a plurality of arc-shaped guides, which have a common mid-point and at least two of which form through slots in the front. A graduated scale extends along the latter guides. The back is transparent in order to make it possible to follow the movement of the movable parts in the casing when the apparatus is used. A pivot pin 4 passes through the mid-point of the guides transversely through the casing. An operating arm 11, two links 22, 25 that form the sides of a rhombus, and preferably also an indication arm 28 are mounted around the pivot pin in such a way that they can be turned. At the end opposite to its axis of rotation, the first 22 of the links is connected to a third link 19 by means of a pivot pin in such a way that it can rotate, which has an indicator that extends through one of the slots in the front and interacts with the graduated scale. The other end of the third link is attached to the operating arm 11 by means of a pivot pin in such a way that it can rotate. This has also an indicator, that extends through one of the slots in the front of the casing and interacts with the graduated scale. By means of a pin, slide or the like 15, the operating arm 11 is connected to a slide arm 14, which at one end has a guide 16 extending in the longitudinal direction of the slide arm, in which the slide 15 can move. The other end of the slide arm has a pin 17 which can slide in a second linear guide 9. At a point on the slide arm located between the slide 15 and the latter pin 17, the slide arm is connected to the end opposite to the pivot pin 4 of the second 25 of the two first-mentioned links by means of a pivot pin 26 which forms the fourth corner point of the rhombus. This pin is movable in one of the arc-shaped guides. From the above, it follows that the angle between the operating arm 11 and a line extended from the second linear guide 9 through the pivot pin 4 is three times as large as the angle between the first link 22 and the said extended line. If the apparatus is supplemented by an indication arm 28 that can be rotated around the pivot pin 4, which indication arm is connected to the operating arm 11 and the first link 22 in such a way that it constantly halves the angle between them, and which has an index interacting with the graduated scale, it is possible by means of the apparatus to demonstrate the division of angles (that are less than 90 degrees) into two or three equal parts. IMAGE
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