Full Details

Name and Model Number Sexton's Omnimetre No. 1
Country of Origin England
Date of Manufacture 1897-1910
Front Scales L, A [B, squares, cubes, secants, sines, tangents, vers sines]
Back Scales None
Scale Length 18.3 cm diameter
Type of Rule Disc
Construction Cardboard
Area of Use Generic
Rarity RR
Donor Collection of Rod Lovett
Match Number 22

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.