Gram motor speed indicator disk scans
This cardboard is disk approx 12cm diameter, published by Bernards and cost 10p back in the 70s.
It relies on the slight flicker of filament lamps to give the strobe effect, 50Hz one side and 60Hz the other side.
Scans attached, 600DPI.
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Paul Stenning
Forum Admin/Owner and BVWS Webmaster
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