Digital indicator (drop gage) works

Your question is a little vague, but the types of glass slides I've seen and used for measurement purposes, are diffraction gratings from which moire fringes can be used to interpolate between the fringe widths, allowing much higher resolutions to be obtained.

1 micron is easy some can be interpolated to 0.1 micron and better!!

John.

I'll take a stab at this slightly general question. Only because I'm boning for a 'good answer' mark

A glass scale such as is used in DRO's and the likes is pretty simple. An extremely precise lay out of incremental marks is laid out on and embedded between 2 panes of glass. Some of these incremental, embedded scales are conductive (older) and some are simply light absorbing (a dark mark).

The scale is fixed and a reader or encoder(?) passes over the scale. The reader is oriented to a zero datum and counts marks as it moves. Some (as I recall) use light or laser technology (photodiode?) and others read by use of an electro magnetic means as it passes over the conductive marks.

The above is for a linear device though a rotary would be most similar in it's workings.

This is the general workings as my memory serves to a rather general question. Hope it helps.

cr3

I suspect I should get a 'B' if this is schoolwork.