"Trane Ductulator", English and SI Metric Units, designed and manufactured by the staff of Trane Company, La Crosse Wisconsin.  Copyright 1976, The Trane Company.  They designed, manufactured and dispensed the item.  Note - the photos you see are of this circular slide rule - no 'Stock Photos'.

A splendid calculator from near a half-century ago, allowing engineers to calculate the amount of air available via an air transfer system.      A clean calculator - apparently never removed from the cardstock sleeve.  

Multicolor, 10" x 7 3/4", with wheels on both sides - one side for English measurment units, the other side for SI Metric units.  Contained in a black/white cardstock sleeve.  

Found in a northern Ohio farmhouse library - 200 years and more of books and paper - they loved, and kept, all their books and paper.  We gathered eight pickup truckloads from that library - bringing all of it to you via eBay now.

No wear, No looseness, No mustiness, No smoke smell.  We do try to describe them correctly - we want you back - hundreds of repeat customers.