- visually (mostly up to 1990): accuracy 0,1" to 2" (depending on the instrument); timing with digital clocks about 0,05–0,2 seconds
- by CCD and other electro-optical sensors: as above, time often better
- semi automatic instruments: Photography or "impersonal micrometer", ca. 2 times better than No.1
- by Scanning methods: Astrometry satellites like Hipparcos about 0,01".
- Accuracy and precision
- Instrument error
- Meridian circle
- Minute and second of arc
- Transit instrument
- Karl Ramsayer, 1969: Geodätische Astronomie, Vol.2a of Handbuch der Vermessungskunde, 900 p., J.B.Metzler-Verlag Stuttgart.
- Ivan I. Mueller, 1969: Spherical and Practical Astronomy as applied to Geodesy, 610 p., Fred.Ungar publ., USA
- IAU Coll.48: Modern Astrometry, Egermann, University Vienna.
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