Dragonfly

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The equestrian level or riding level ( striding / reversible level ) is an instrument for the precise leveling of geodetic theodolites and astronomical universal instruments .

Scheme of an equestrian vial, including an adjustment device. The notches of the two supports are perpendicular to think to the plane.

It is a tubular vial , which is not permanently built into the alidade , but is placed directly on the tilt axis with two precisely ground metal supports . The length of the glass scale is about 5–8 cm, the size of the air bubble 1–2 cm. Their advantages over Alidaden dragonflies are:

  • a higher accuracy: pars values from 2 to 5 "instead of about 20"
  • better readability in both circular positions
  • no influence from any bends or temperature effects on the theodolite.

The disadvantage is the additional price and the fact that the rider dragonfly can fall off due to carelessness. Some manufacturers prevent this with notches at the bottom of the supports. These must have a certain height so that the telescope can be penetrated underneath.

Rider vials can usually - for the direct determination of the tilt axis inclination - be repositioned by 180 °. However, one must ensure that there are no dust particles on the two exposed points of the tilt axis.

Large universal instruments (e.g. the Wild T4 ) and passage instruments use hanging vials instead of rider vials . In the case of the T4 and the Askania Transit, they are around 20 cm long and par values ​​are even less than 1 ". That is why they are also called second levels .

For fully electronic theodolites, riding vials are usually no longer available, as they are equipped with inclination sensors . However, measurements must be made in both circular positions in order to exploit their potential.

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