I don't know much about this item, it was in a cupboard at my Dads place for quite some time. There's no makers name visible, I don't know what the little knob on the back is for, maybe to lock the tell tale up? Anyway, it is what it is. This item is in the category "Antiques\Science/Medicine\Scientific Instruments". The seller is "mushypea63" and is located in this country: GB.
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