Full Details

Name and Model Number Aristo 920 Federfix
Country of Origin Germany
Date of Manufacture  
Front Scales Many specialised scales and curves
Back Scales None
Scale Length 34.6 cm maximum
Type of Rule Instrument
Construction Plastic
Area of Use Technical
Comment Used in the computation for cylindrical coiled springs.
Rarity RRR
Donor Collection of Rod Lovett
Match Number 9

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.