Full Details

Name and Model Number Dempster RotaRule
Model A
Country of Origin USA
Date of Manufacture 1928 to ~1930
Front Scales B Gh Gv CT T S'T' CS S CIF CI C D A K
Back Scales L LL1 LL2 LL3 (unmarked = long C) V1 V2 (unmarked long D)
Scale Length 50" (127cm)
Type of Rule Disc
Construction Plastic 5.25" (13 cm) diameter
Area of Use Other
Comment For precision basic math and stadia calculations. Has unique modified spiral scales. In about 1930 with serial number 426 model A was upgraded to model AA with 3 additional scales - see model E image believed to be experimental transition to model AA. Note #426 transistion image courtesy of Dempster Family.
Rarity RRR
Donor Collection of Richard Davis
Match Number 66
(Click Picture for Details)

In conjunction with our 'donors' we assign a rarity rating to each item, based on the system devised by Herman van Herwijnen
(1929 - 2004), renowned Dutch collector, author, and creator of Herman's Archive, a collection of 5,000 slide rule images on CD.
• RR = Rare - 1 of 25 collectors has one; it may take a year to find an example in the marketplace.
• RRR = Very Rare - only a few known to collectors; may be several years before it comes up for sale.
• RRRR = Extremely Rare - a museum piece; unlikely that an example will come up for sale.