touchmark

plural touchmarks · alternative touch-mark

1. archaicThe manufacturer's official identifying sign, impressed into a pewter object.

   For quality control, Parliament in 1503 required all London-made pewter to be stamped with the maker's symbol or touchmark.

   1988 Dec. 1, Susan G. Sawyer, Photog Pewter the Time-Honored Way," New York Times (retrieved 5 July 2012)

2. archaicrareA symbol, sign, or other inscribed indication used to aid the alignment, calibration, or other adjustment of a measuring device or scientific instrument.

   The initial touch-mark was established at Roper's saw-mill, on the North River, and is a point on 20-penny nail driven flush with the horizontal surface of sill to bull-wheel.

   1880, "Survey of the Albemarle and Chesapeake Canal", Report of the Chief of Engineers U.S. Army, page 864

   1 more example

   The instrument used was a refracting telescope by Dollond. . . . The cap containing the diaphragm was furnished with a touch-mark consisting of a projecting spoke. When in adjustment as described above this mark was parallel to the short side of the parallelogram.

   1876, W. H. H. Hudson, “On Observations made at San Antonio on the Total Solar Eclipse of 22 Dec. 1870”, in Proceedings of the Cambridge Philosophical Society: Mathematical and physical sciences, Volume 2, pages 205–6