It is set in position and the amount of its projection beyond the edge of the sector is measured by means of the micrometer screw-gauge shown in fig.

4.

The screw-gauge is used in the following manner: it is adjusted so that the distance of the surface D from the surfaces BB is equal to the amount which it is required that the strip should project ; it is then placed so that the surfaces BB rest against the edge of the sector and the strip is pushed up to the face D.

And fixed there.

In the first few experiments the projection was always re-measured after rotation of the sector, but after a little practice in the use of the apparatus had been gained this was found to be unnecessary.