Over the 19th and much of the 20th centuries the slide rule was the primary instrument for calculation used by many people engaged in the trades and in engineering. Although originally invented in the 17th century, and widely used for gauging (or estimating the quantities of certain products such as spirits) it took until around 1850 for them to become generally popular with those for whom mathematics was a daily task. This was largely brought about through the increase in accuracy made possible by the development of the dividing engine and Amédée Mannheim's 1850 standardisation of the arrangement of scales utilised. His scales were the "C" and "D" scales, ranging from 1 (the index) to 10 and used for multiplication and division, and the "A" and "B" scales, ranging from 1 (the index) to 100 and used for squares and square roots.

New arrangements of scales appeared in the 20th century with the Rietz arrangement in 1902 and the Darmstadt arrangement in 1934. The Rietz scales added a log "L" scale, a "CI" or C inverted scale which was useful for calculations involving the reciprocal of a number, and the trigonometric scales: sine "S", tangent "T" and "ST" for the small angles were the sine and tangent are the same, to the front face of the stock. The Darmstadt arrangement added a series of Log-Log scales.

This slide rule was manufactured by Johan Faber AG in the early 20th century using the techniques that had been developed in the family company, A.W. Faber based in Stein near Nurnberg, Germany. Slide rules manufactured by Johan Faber, A.W. Faber and Faber-Castell were among the best made and most successful slide rules of the 20th century. The Faber company began as a maker of lead pencils in 1761 and expanded during the following century until in 1862 the then head of the company Lothar Faber was made a peer by King Maximilian of Bavaria, becoming Lothar von Faber. At this time the A.W Faber Company began to expand their product range. Lead pencils remained their main product until, in 1882, they commenced the manufacture of wooden slide rules using the Mannheim scales, selling them in Germany, France, England and the United States.

Lothar von Faber's brothers, Eberhard and Johan, were sent to North and South America (respectively) to establish new markets. However in 1876 Johan set up his own company in Brazil and about the same time Eberhard established his Eberhard Faber Inc in the United States, both to compete with A.W. Faber still in Germany. Johan Faber's company subsequently also manufactured slide rules in Germany. In the 1930s the two competing companies were merged with A.W. Faber under the name Faber-Castell.

A.W. Faber stopped making slide rules in 1976 since the electronic calculator had taken over the market for hand-held calculating instruments.

Refs:

Peter Hopp, Slide Rules, their History, Models and Makers, Mendham, New Jersey: Astragal Press, 1999.

http://www.answers.com/topic/a-w-faber-castell-unternehmensverwaltung-gmbh-co?cat=biz-fin - Company History: A.W. Faber-Castell Unternehmensverwaltung GmbH & Co.
Time Line for A.W. Faber and Faber-Castell

http://www.sliderulemuseum.com/SR_Dates.htm#Faber - Dieter von Jezierski, Slide Rules - A Journey Through Three Centuries (Astragal Press).

Stephen Jones
17 January 2008

Johan Faber, model 9205
Mfr date: early 20th C

There were generally two types of slide rules. One type were the linear slide rules consisting of a pair of strips of timber faced with celluloid (and in the mid-20th century, plastic) forming what is known as the "stock" and with a sliding strip inset between them. Of these there are two sub-types: closed frame, which is usually single-sided and appears as a single body of wood or plastic, and open frame, in which the stocks are separate but held together by straps usually of metal at each end of the body. The other type were the circular slide rules consisting of two or three concentric disks. Each type could have several sets of scales applied to them. Most slide rules have some kind of cursor which can be slid along the rule (or around the disk) acting as an indicator that assisted in lining up the slide scales with the scales on the stock.

This slide rule is of the linear closed frame type. It was manufactured by Johan Faber AG in Germany

Slide rule, closed frame, single-sided, double-sided slide, celluloid laminate on boxwood, metal-rimmed glass cursor, edge rulers. Scales engraved into celluloid. Whole structure held together by 6 fine screws. Top edge of stock is bevelled with a 26 cm ruler. Bottom edge has a 10 inch ruler. Paper chart of conversion tables and useful data on reverse.

In black card slip-case.

Johan Faber, model 9205
Mfr date: early 20th C

Scales:
Stock, upper: K, A
Slide, obverse: B, C
Slide, reverse: S, L, T
Stock, lower: D, 10 inch

Made: 1900 - 1925

Model number on slide channel, in center (slide over to see), printed in black ' Johann Faber No. 9205 / System Rietz '. White paper label on reverse, handwriten in black ' Bromely 1982-73 '.

2010/1/313

1900 - 1925

295 mm

20 mm