Tick mark
As graduation in is metrology and geodesy the exact division of standards, setting circles and other measuring equipment referred to in the form of regular, short strokes or geometric pattern. In the case of linear measuring equipment, the graduation marks are arranged parallel, in the case of pitch circles, they are arranged radially.
Since the measuring accuracy depends essentially on this scale division , it is carried out by special, very precisely calibrated machine tools . It is this
- Length dividing machines for precise rulers , measuring triangles, thermometers , etc., but also for leveling and measuring staff , or
- Circle dividing machines for protractors, for pitch circles of theodolites, of astronomical telescope mounts etc.
For glass rulers or the partial circles of geodetic measuring instruments, etched or photomechanically produced scales have been used since around 1950 . With the digital generation of instruments, the reading is opto-electronic using a phase grating or moiré pattern . The measuring equipment also contains reference marks for incremental encoders .
In the case of prism rulers , protractors and other common construction aids , the graduation is accurate to about 0.03 mm, with optical micrometers to a few 0.001 mm (a few µm ). In theodolite or astronomical meridian circles pitch accuracies of at least 1 "( angular second required).
See also: reading , pattern recognition