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  Surveying Instrument Collection 


E. R. Watts & Son, London, England



Serial Number



Height 640 mm, telescope length 415 mm


E. R. Watts & Son Micrometer TheodoliteE. R. Watts & Son Micrometer Theodolite


This micrometer theodolite played an important role in history and is probably one of the most valuable instruments in the collection due to its role in setting out the Sydney Harbour Bridge in the late 1920's. It is a 2" first-order theodolite with a 215 mm diameter horizontal circle and was primarily used for first and second-order triangulation and traversing. The theodolite features a ball-bearing in the vertical axis, a rotatable horizontal circle, a conical bearing for the horizontal axis, a clamp-block assembly and diametrically opposite 'Ramsden' eyepieces. The horizontal and vertical circles are completely enclosed in order to protect the graduations from dust and grime. The circles are graduated to 10 minute divisions and the readings are taken through two micrometer eyepieces placed 180 degrees apart on the alidade. The degrees and minutes can be read directly off the circles, while for greater accuracy the micrometer will give readings directly to 2 seconds and estimations to 0.5 of a second.

The plate level (No. 317) has a sensitivity of 12"/2 mm, the altitude bubble (No. 307) one of 3.9"/2 mm and the striding level (No. 302, Pat. No. 207871) one of 2.5"/2 mm. The weight of the instrument is about 24 kg, without transport box. The foot plates fit into a circle of 150 mm diameter and the rotating parts into a circle of 215 mm radius.

History & comments

The instrument is a very important historical theodolite, since it was used by surveyor E. A. Amphlett for setting out the Sydney Harbour Bridge between 1925 and 1931. It was exhibited at Science House, Sydney in 1932. Since 2003 the instrument is on loan to BridgeClimb. Between 2003 and 2009, it was exhibited in the (SE) Pylon Lookout Exhibition of the Sydney Harbour Bridge. Since September 2009, the instrument can be viewed in the Sydney Harbour Bridge Museum at the entrance to BridgeClimb in Cumberland Street, Sydney.


In a box


Good condition, well preserved



Traversing Target

  • The theodolite includes two Traversing Targets, one of which is shown in the image on the left. The two targets are labelled as Target A (No.10126) and Target B (No.10127). The actual target is an 80mm diameter circular glass plate with engraved cross-hairs for targeting, and the base of the targets can be shifted for centring purposes.
  • Traverse targets were designed by D. L. Parkhurst of the U. S. Coast & Geodetic Surveying Department
  • Information on the 'surveys for the design and layout of the Sydney Harbour Bridge' can be found in the paper by W. Burrell in the journal 'The Australian Surveyor', September 1963, pp. 395-403
  • According to David Griffiths (22 April 2003), details of the theodolite and the surveys are still being held by the decendants of E.A. Amphlett
  • Catalogued by T. Ko
  • Updated by F. Pall & J.M. Rüeger


Manufactured in 1924 (approx). Catalogued in 1997, 2005 & 2010.

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