Saw these at work and thought others here may be interested as it represents a way to make your own accurate height gauge.
This is from work - we have two, a metric and imperial but the principle is the same
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They are called 'Microball' because they use a stack of ball bearings in the column to give position - 10mm balls for the metric version and 1/2" balls for the imperial version
(Sorry - next two photos are not all that sharp)
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The knob on the back is attached to a wedge, so to adjust the height, the knob is loosened, moved to the appropriate number on the side of the main column and then screwed in. The wedge self centres on the 'valley' between the two balls. As ball bearings are accurate to somewhere near micron levels, the head on the column is positioned to a fair degree of accuracy.
The scriber slides in the head and is pulled upwards with a spring (cover piece removed for photo). A micrometer head is then used to push down on the scriber.

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In use, the head would be positioned to the most convenient major division and then the micrometer head wound up or down until the desired value is achieved. A very elegant way of getting accuracy. Micrometer heads are not all that expensive (if necessary, buy a cheap micrometer...) and a stack of ball bearings means that the rest of the lesser precision components can be made in the workshop.
This technique could be adapted for any size height gauge, or indeed anywhere where precise measurement is needed

Michael
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