| The glass is ground with emery to the correct spherical figure as given by a spherometer. |
| Before the grade of emery is changed all three surfaces must agree, as nearly, at least, as the spherometer will show. |
| The squares of glass are cemented to the roughing tool, and this is ground to the spherometer by means of the counterpart tool. |
| It is well to control this process by means of a spherometer, so that the desired radius may be approximately reached. |
| The spherometer is accepted at all stages of the process as the final arbiter as to curvature. |
| He made adaptors to convert Barker's RAS-thread eyepieces to push-fit, to the latter's delight, plus a fine spherometer for the mirror-maker Jos Slater. |
