Description

A GPM3 Parallel-Plate Micrometer. The micrometer is an accessory for use with a Wild (or Leica) NA2 universal automatic level to facilitate precise levelling. The GPM3 is fitted onto the NA2 telescope objective and locked in position with the knob (4). By turning the micrometer knob a parallel-sided glass plate is tilted, thereby causing the line of sight to be raised or lowered. The range of displacement is 10mm. On the scale, seen in the GPM3’s eyepiece, the amount of displacement is read directly to 0.1mm and estimated to 0.01mm.

   1 Micrometer knob

   2 Open sight

   3 Housing of parallel plate

4 Knob for locking GPM3 in position

The micrometer was used in the Concrete Laboratory at Heriot-Watt University, Edinburgh, UK.