Depth measurements

First post, I was looking for a microscope device to measure precise X-Y distances (plus-minus 0.0001" or 0.0025 mm, or so), commonly known as a “toolmakers” microscope. I noticed on-line, there are “vernier microscopes” that appear to measure depth as well (photo attached of an example). This would be very useful to me, I do engraving. I would guess this is accomplished by focusing adjustments, i.e. focus on one area, read the scale, then focus on another area, and compare. If this is the case, is there any idea as to what accurate to expect? Thanks.

Is the question how sensitively you will be able to measure if something is in focus or not? This will depend on the depth of focus of the microscope, which is not obvious from the picture. Do you have any more information such as the NA (numerical aperture)? Focal length? Magnification? Here is one resource that might help answer your question:
Nikon Depth of Focus Tutorial.

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Thank you for the reply; the application is to engrave brass dies to a depth of 0.050", which will be used to cast letterpress printing type. So if I have a known standard that is 0.050" deep, I then want to compare it to a newly engraved piece. In the vernier microscope above, I would inspect a new engraving; if it was out of focus, I would then move the lens assembly up or down until it comes back into focus, then read the vertical distance. Comparing the “start” with the “finish” position tells me how far out the new engraving is from the standard. The big question is then, what is the accuracy of the reading? If it is very precise, it will be very useful; so good to know before I buy something of this type. From your response, I can see without more detail, it is not a simple answer.