How do I check an angle with the reversal measurement?

The reversal measurement, often referred to as the reversal method, is a very simple and accurate method of checking the accuracy of a 90° angle. The reason why the reversal measurement is so accurate is that the accuracy of the measurement does not depend on a second test angle. A plate with a straight edge, a pencil and a calliper are all that is needed for this simple method. This method can be used to check all angles, e.g. carpenter's squares, joiner's squares, locksmith's squares, bricklayers' squares and many more.

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Why doesn't the carpenter's square have a right-angled end?

In the past, it was common to decorate window frames and doors with stucco. This can still be admired on many old buildings today. The curved end of the carpenter's square possibly served as a kind of template and thus helped in the production of the decorative frames.

The picture shows a carpenter's square as they were made in the Ernst Haas factory in Wuppertal until around 1965 and the profile at the end of the square that was common at the time.

To make the brackets, 5 mm thick material was heated red-hot in a forge and drawn to the desired length with a forging hammer. This gave the long leg of the carpenter's square the conical shape that was common in the past (tapering from 5 to 2 mm). The legs were then cut to width and finished with a whetstone. The curved end was stamped with a punch on the press.

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