National Physical Laboratory

Where can I get my theodolite calibrated? (FAQ - Length)

There is no simple answer to this question, since calibration for a theodolite can mean different things to different people.

For normal land-survey use, where a pair of theodolites are used, combined with 'face-left/face-right' measurements, then theodolites are, essentially, self-checking and do not require calibration.

If a single theodolite is used for simple measurement of angle, then there are various parameters that can be checked:-

  • The de-centring of the circles - this is something that is self-correcting if the theodolite is used for two-face measurement.
  • The zero of the vertical circle being at right angle to the horizontal circle - this is something it is easy for the user to check and adjust (many theodolites have a knob to let the user adjust this).

The accuracy of the angular scales themselves is very difficult to check - the horizontal circle can be compared to an indexing table and fixed collimator, but it is extremely difficult to set up a system to check the vertical circle.

The straightness of the line of sight (i.e. does the telescope point in the same direction as the focus is changed) is virtually impossible to test.

The only UK laboratory that is UKAS accredited for the calibration of theodolites is Falcon Scientific Instruments of Union Terrace, York. They offer a check of the circle centring and collimation errors - something competent end-users can do for themselves.

Details of Falcon Scientific can be found on the UKAS website.

Last Updated: 25 Mar 2010
Created: 17 Jul 2007


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