Hans Gruber (or Gruwer) worked in Nuremberg as a clock maker. He was registered as a master locksmith in 1552 and made clocks, watches, sundials, astronomical compendia and gunnery instruments dating between 1565 and 1583. For adjusting his sundials to the vertical he adopted the 'needle-level' invented in 1552 by his fellow-citizen Christian Heiden. Gruber's maker's mark is HG with crossed spades within a shield.
E. Zinner, Deutsche und Niederl?ndische astronomische Instrumente des 11. bis 18. Jahrhunderts (2nd ed., Munich, 1967), p. 327; P. Gouk, The Ivory Sundials of Nuremberg 1500-1700 (Cambridge, 1988), pp. 64-5.
Sun And Moon Dial, Signed by Hans Gruber, Nuremberg, circa 1570 (Oxford, MHS)