[Fig. 1374] shows the circle turned half-way round, the points 0 and 128 coinciding with the cross threads of the microscope.
Fig. 1375.
[Fig. 1375] shows a similar reading, in which the points do not coincide with the cross threads of the microscope.
Fig. 1376.
[Fig. 1376] shows the microscope adjusted for testing by turning the circle a quarter revolution.