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  Surveying Instrument Collection 


Wild, Heerbrugg, Switzerland


GDP 1 (?)

Serial Number



36 mm diameter, 70 mm high (closed), 82 mm high (opened)



This double pentaprism (optical square) allows to set out right angles, to determine a point on a line and to drop a perpendicular from a point onto a line. Points are usually marked by (red-and-white) ranging poles.

The instrument at hand has a window at the top that directs the view to the left, a window at the bottom showing the view to the right. There are two windows to see straight ahead, namely the right most quarter of the upper window and the left most quarter of the lower window. Presumably, one has to sight over the top to the point ahead if a perpendicular is to be dropped on a line.

In the closed position, a plumbbob can be attached to a hook at the bottom of the handle. In the open position, the cover and handle screw down and cover the plumbob hook. The hollow handle (8 mm diameter) allows attachment to a plumbing rod.

The shell of the device is made from brass and painted black.

History & comments

Manufactured before 1972. From 1972, Wild Heerbrugg advertised a newer and lighter version GDP2, featuring see-through windows above and below the two pentaprisms and a rotatable cover. Weight 60 g. An extendable plumbing rod GLS4 (0.9 kg) was then offered.


no box


some paint damage


Top surface engraved with "Wild Heerbrugg Switzerland"

Labelled with white paint "Uni NSW 11"


Catalogued on 9 Oct 2014 by JMR. Photo by JMR.

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