10. Measurement of Indentation
10.1 The accuracy of the test method depends to a very
large extent on this measurement, as follows:
10.1.1 If the measuring system contains a light source, take
care to use the system only after it has reached equilibrium
temperature. This is because the magnification of a microscope
depends on the tube length.
10.1.2 Carefully calibrate the measuring system with a stage
micrometer or, better, with a grating.
10.1.3 If either a measuring microscope or a filar micrometer
is used, always rotate the drum in the same direction to
eliminate backlash errors.
10.1.4 Check each reading twice. They should reproduce to
60.0002 mm. One filar unit is equal to about 0.0002 mm when
a 503 objective is used in conjunction with a filar micrometer
that has a millimetre scale and a 100-division drum.
10.1.5 Use the same filters in the light system at all times.
Usually a green filter is used