With the problem of longitude determination Mayer became known during his work at the Homann map publisher in Nuremberg. Tobias Mayer found that for longitude determination at sea (and on land) only those methods can be of practical importance, which are based on the meeting of the moon on its monthly orbit around the earth with stars standing on this stripe of heaven. In order to improve the method of length determination, it was necessary to have a very precise knowledge of the movement of the moon, the calculation of its position, which he could summarize as a result of his work in a table. For finding the exact position determinations in the sky Mayer invented the repetition principle), which he realized in the design of a repetition circle (which he called “Astrolabium“). For the angle measurement on the telescope Mayer developed a new type of micrometer, which he used on various instruments.