Full Details

Name and Model Number Sexton's Omnimetre
Country of Origin England
Date of Manufacture 1895+
Front Scales L, A [B, secants, squares, sines, cubes, tangents, fifth power, vers sines]
Back Scales None
Scale Length 18.1 cm diameter
Type of Rule Disc
Construction Cardboard
Area of Use Generic
Rarity RR
Donor Collection of Rod Lovett
Match Number 25

RR = Rare -- 1 of 25 collectors has one; it may take a year to find an example in the marketplace.   
RRR = Very rare -- only very few known to collectors; may take several years before one comes up for sale.   
RRRR = Extremely rare -- a museum piece; unlikely that an example will ever come up for sale.