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  Surveying Instrument Collection 


B. A. C. (British Aircraft Corporation) Division Stevenage



Serial Number



Telescope Length 310 mm, Height 670 mm (height of theodolite + gyroscope)


B.A.C. Gyro TheodoliteMeridian Indicator


The instrument pictured above is typically used by the military. Their principal application is in mining, tunnelling and gunnery, but in conventional surface surveys they can be used to provide initial orientation, in place of magnetic bearings or astronomical azimuths.

The instrument shown at the top is referred to as a 'gyro-theodolite'. It basically consists of a gyroscope attached to the bottom of a Hilger & Watts micrometer theodolite. The gyroscope enables the direction of true north to be determined with a standard error of about 15" within a very short time. The instrument shown on the bottom is a 'meridian indicator' (also known as a Precision Indicator of the Meridian) which is connected to the gyroscope and includes external connection to the power supply. It is basically a meter graduated directly in angular units, and the reading is thus a maximum when the gyro is pointing north and a minimum when it is pointing east or west.

The theodolite remains permanently attached to the gyro assembly. The gyroscope unit is suspended in vertical gimbals, which lie in the line defined by the downward extension of the (permanently) attached theodolite. The actual gyroscope is floated in liquid, and it is called a floating gyroscope to distinguish it from the pendulous type in which the gyroscope unit is suspended and hangs under gravity.

History & comments

Any solid body, undergoing any rotation can generally be considered as being a gyro. Its fundamental characteristics are its inertia and its precession (directional change due to external moments acting on its rotational axis).


The theodolite is covered with a metallic lid when not in use





  • Catalogued by T. Ko
  • Updated by F. Pall


Manufactured in 1966 (approx). Catalogued in 1997.

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