1. visually (mostly up to 1990): accuracy 0,1" to 2" (depending on the instrument); timing
   Timing
   Timing is the time when something happens or the spacing of events in time. Some typical uses are:* The act of measuring the elapsed time of something or someone, often at athletic events such as swimming or running, where participants are timed with a device such as a stopwatch...
   
    with digital clocks about 0,05-0,2 seconds
2. by CCD
   Charge-coupled device
   A charge-coupled device is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time...
   
    and other electro-optical sensors
   Electro-optical sensor
   Electro-optical sensors are electronic detectors that convert light, or a change in light, into an electronic signal. They are used in many industrial and consumer applications, for example:* Lamps that turn on automatically in response to darkness...
   
   : as above, time often better
3. semi automatic instruments: Photography
   Photography
   Photography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film...
   
    or "impersonal micrometer", ca. 2 times better than No.1
4. by Scanning
   Scanner
   Scanner may refer to:* WikiScanner, a tool that provides a searchable database of anonymous Wikipedia edits* A personality type described by self-help author Barbara Sher-Technology:* Scanner , for searching for and receiving radio broadcasts...
   
    methods: Astrometry
   Astrometry
   Astrometry is the branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. The information obtained by astrometric measurements provides information on the kinematics and physical origin of our Solar System and our Galaxy, the Milky...
   
    satellite
   Satellite
   In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....
   
   s like Hipparcos about 0,01".

Literature

• Karl Ramsayer
  Karl Ramsayer
  Karl Ramsayer was a German geodesist and is well known as one of the most important scientists in geodetic astronomy and in electronic navigation....
  
  , 1969: Geodätische Astronomie
  Geodetic astronomy
  Geodetic astronomy is the application of astronomical methods into networks and technical projects of geodesy.The most important topics are:* Establishment of geodetic datum systems Geodetic astronomy is the application of astronomical methods into networks and technical projects of geodesy.The...
  
  , 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
  International Astronomical Union
  The International Astronomical Union IAU is a collection of professional astronomers, at the Ph.D. level and beyond, active in professional research and education in astronomy...
  
   Coll.48: Modern Astrometry
  Astrometry
  Astrometry is the branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. The information obtained by astrometric measurements provides information on the kinematics and physical origin of our Solar System and our Galaxy, the Milky...
  
  , Egermann, University Vienna.

See also

• Meridian circle
  Meridian circle
  The meridian circle, transit circle, or transit telescope is an instrument for observing the time of stars passing the meridian, at the same time measuring its angular distance from the zenith...
  
  
• Passage instrument
• Theodolite
  Theodolite
  A theodolite is a precision instrument for measuring angles in the horizontal and vertical planes. Theodolites are mainly used for surveying applications, and have been adapted for specialized purposes in fields like metrology and rocket launch technology...
  
  
• angular measurement
  Angle
  In geometry, an angle is the figure formed by two rays sharing a common endpoint, called the vertex of the angle.Angles are usually presumed to be in a Euclidean plane with the circle taken for standard with regard to direction. In fact, an angle is frequently viewed as a measure of an circular arc...
  
  
• accuracy
• Accuracy and precision
  Accuracy and precision
  In the fields of science, engineering, industry and statistics, the accuracy of a measurement system is the degree of closeness of measurements of a quantity to that quantity's actual value. The precision of a measurement system, also called reproducibility or repeatability, is the degree to which...
  
  
• Instrument error
  Instrument error
  Instrument error refers to the combined accuracy and precision of a measuring instrument, or the difference between the actual value and the value indicated by the instrument . Measuring instruments are usually calibrated on some regular frequency against a standard...
  
  s
• Arc seconds
• angular mil
  Angular mil
  An angular mil, also mil, is a unit of angle. All versions of the angular mil are approximately the same size as a trigonometric milliradian.-History:The milliradian was first identified in the mid nineteenth Century...