I bought one that is metric and (nominally) reads in 0.01mm increments - it was about £20 and having used it quite a lot already I would say that it is superbly made and well-worth this price-tag. It performs the task for which I bought it to my complete satisfaction and in excess of my desired performance-level - in short, I love it!
I've used it to make some quick, easy and accurate measurements of a selection of different cover-slips of different sizes and thicknesses (specified not accidental that is), new high-quality slides and the same slides with fully-dry and permanently mounted specimens with cover-slips upon them - the results I think show the micrometer to be a superb and accurate piece of kit.
It's very easy and quick to use, consistent and accurate to about 0.002mm I would say, as it's calibrated to 0.01mm with the usual lines on the barrel, but it is easy to literally 'read between the lines' (i.e. interpolate visually) with what I would estimate to be a reliable and useful accuracy of about 0.002mm!
Here's the beauty with it's shiny-new box...
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I thought I'd try a quick run with it as follows, the intention being to mount 2 coverslips without sections just plain cover-slips mounted with 'Numount', the resinous mountant I always use. One had a wooden mini-peg placed upon it during a 26hr drying time, the other didn't - to see if this applied weight made any difference to the dried thickness of the whole thing, measured as slide+coverslip_mountant-layer between them.
Of course the hypothesis was that the mount with added weight would finish drying as a thinner and therefore more desirable mount than the one dried without weight applied....
To make the test more reliable I should measure and use 2 seperate slides, 1 for each cover-slip, making sure that each spot used on each slide was of identical thickness and similarly each cover-slip was of the same thickness - I didn't go to that length as this was as much a practice for the use of the micrometer as for this test, although at a later time I would be interested to run a similar series perhaps even using sections mounted within the mountant, anyway this is the basic test in it's imperfect but still useful I think form...
I measured a slide's thickness in 2 spots, with the intention of mounting (side-by-side) 2 cover-slips, each centered on one of these spots, a & b.
Nominally these slides are 1mm, the actual measured (2) spots along it's long-axis measured,
spot a on the left = 1.018mm, spot b on the right = 1.013mm, reasonably close to their stated 1mm, not really relevant in use but needed to know this for this comparative test.
The 2 cover-slips A on the left and B on the right measured (in their centers) 0.169mm and 0.183mm respectively. This gives a theoretical (and probable) thickness total of 1.018 + 0.169 = 1.187mm before mountant for the left side mount
and 1.013 + 0.183 = 1.196mm for the right...
Measured after 26hrs drying time, the left-hand mount with weight applied throughout, the 2 sides measured as follows,
on the left the total thickness of slide(1.018) + mountant(call this as yet unknown 'ma') + cover-slip(0.169) = 1.193mm,
so the mountant-layer (ma) must be 1.193-(1.018+0.169) = 0.006mm or 6µ, and for the right-hand mount we do the same,
On the right the total thickness of slide(1.013) + mountant(call this as yet unknown 'mb') + cover-slip(0.183) = 1.205mm,
so the mountant-layer (ma) must be 1.205-(1.013+0.183) = 0.009mm or 9µ...
So we have the mount on the left, with added weight, at a final dried thickness for the mountant only of 6µ, and the mountant only of the right-hand mount without added weight drying at a thickness of 9µ.
It's perhaps possible to tentatively suggest two things I think:
a) - the addition of weight during drying reduces the thickness of the finished dry layer of mountant.
b) - the degree of reduction may in this case at least be expressed as approx 33% (i.e. 3/9)..
Not the most disciplibed or valid of tests of course, but I think the basic principle may be accepted and worthy perhaps of a more controlled series of tests with standard sizes and multiple test-subject beyond just 2 on the same slide!
Good practice anyway for my micrometer, which I'm already using to sort my cover-slips into the 0.17mm for which my 'scope's objectives are labelled as calibrated... Every little helps with results!
Measuring further into the micrometer's usable range to see how it returns to zero from here... 4.953mm measured here..
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Thanks zz' for your interest.
) each of which gives me different-sized drops, and above all, consistently so I find.