German mathematician and instrument-maker. In 1518, during a visit to Italy, struck up a friendship with Andreas Copernicus, Nicolaus's brother. Hartmann sought to measure magnetic declination, for which he computed relatively good approximations in several localities including Nuremberg and Rome. Made many high-quality mathematical instruments including sundials, astrolabes, globes, armillary spheres, and astronomical compendia, but also military instruments such as gunner's calipers. In 1533, published a manual on the construction of diptych dials. Other, unpublished works contain drawings of scientific instruments such as sundials and astrolabes.