Stuart has been told that this tool is either a heliograph, a scoop for measuring grain or something to do with powder for guns..
With Customs&Excise, anything is possible......
Tom Martin has come up with a very persuasive attribution:
"I have never seen one in the flesh but I suggest that you have a reflector as used in D&F’s hydrometer testing apparatus. Catalogue page attached
Stamped “Custom & Excise” so post-1909, relatively modern."
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