Full Details

Name and Model Number Dennert & Pape I
Country of Origin Germany
Date of Manufacture c. 1890
Front Scales A[B C]D
Back Scales S L T
Scale Length 25 cm
Type of Rule Slide Rule
Construction Celluloid on mahogany
Area of Use Generic
Comment Dennert & Pape was one of the three major German manufacturers of slide rules (the two others being Faber-Catell and Albert Nestler). D&P became known under the name Aristo as from 1936, when they dropped celluloid on wood and began making their rules in Astralon.
This model is one of the early slide rules made using their German Patent DRP 34583. This patent was for laminating white celluloid on wood (though not specifically meant for slide rules).
For dating the rule, I used the clues given by Guus Craenen in his book: Rechenschieber im Wandel der Zeit 1787-1905. Soest. 2009.
D&P began the manufacturing of one sided nose cursors as from 1873. In 1890, the standard cursor was the glass cursor.
DRP patent 34583 was granted in 1886.
D&P began the manufacturing of celluloid plated slide rules in 1888.
As from 1888 the firm's name is engraved in the well.
As from about 1888 D&P dropped the embellishment longitudinal lines (this model bears them though).
As from about 1888 D&P begins to mill a longitudinal groove at the back of the stator to take off the tension (it's not the case with this specimen) and as from 1890 the groove is replaced by a split (also not the case with this specimen).
As from about 1890, the single square cutting at the back of the rule is replaced by a square cutting at both ends. As from 1895, the square cuttings are replaced by rounded ones.
Up to about 1902, D&P slide rules with a length scale of 25 cm had an overall length of 26 cm (the length of this model), which was later changed to 27 cm.
Rarity RRRR
Donor Photo from a collection in Belgium
Match Number 390
(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.