Full Details

Name and Model Number ROSS
Precision Computer
Type II
Country of Origin USA
Date of Manufacture c. 1919-1924
Front Scales Spiral scale in 25 revolutions, L scale at edge
Back Scales Graphical sin & tan tables in 5 winding spiral.
Scale Length 9.14-m
Type of Rule Disc
Construction Spiral scale engraved on a 21-cm dia. stainless steel disk. Accessory small metal slide rule fastened to pivot is used to facilitate the determination of approximate values and to indicate which spiral the precise result is on.
Area of Use Generic
Comment Instructions on handle. Introduced in 1919. This slide rule was made for about 5 years. Only known stainless steel version. Most examples of the Ross Type II have the spiral scale printed on an enameled base metal surface that readily blisters with time. One example is known where the spiral scale is on a brass disk. This example is much heavier that the Type I model.
Rarity RRRR
Donor Collection of Ed Chamberlain
Match Number 123
(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.