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Brief history of "Gamma" slide rules


The best-known slide rule ever made in Hungary is the 10-inch type Gamma 2512. The manufacturer still exists, produces nuclear measuring equipments, was founded under the name Gamma Műszaki Rt. (Gamma Technical Plc.) on 18 May 1920. Before the World War II, they produced mainly precision equipments for surveying, optics and so on, then these were replaced by military equipments. After the siege, they were servicing and manufacturing tools for the Soviet Red Army. Due to political changes, the former CEO was removed, and the company had to produce such things as camera named Pajtás, or the Gamma lighter for surviving the decrease of income. By 1947 the factory was near bankruptcy, so the company was nationalized on 30 July 1947. In 1949, the Gamma Finommechanikai és Optikai Művek NV (Gamma Precision Mechanics and Optical Works National Corporation) makes profit again. Important to note, that Gamma founded a subsidiary named Gamma Finommechanikai Gyártmányokat Árusító Kft. (Gamma Distribution of Precision Mechanic Products Ltd.) in 1936, which selling mainly Gamma-made instruments, but they imported some drawing tools, and slide rules mainly from Germany. So there are many slide rules has the markings "Gamma K.F.T.", but these are not (yet) produced by Gamma.

In the second half of 1940s, the hungarian industrial politics decided that instead of importing expensive foreign slide rules, domestic production has to be started. The Logarex factory in Czechoslovakia was founded in 1951 for similar reasons. The Gamma Works started production of 10-inch aluminium Rietz rule in 1948, but it was replaced by 10-inch wooden Darmstadt slide rule type 2503 (later 2513) in May 1949. Because of this, according to contemporary reports, the "country" saved 1.5 million forints a year.

Then more types was designed and produced, e.g. the well-known 5-inch Rietz pocket slide rule (type 1252), or the Robot, a special machining rule planned for calculating metal cutting speeds, feeds and so on. The production line was moved to Logarléc és Mérőszalag Üzem (Slide Rule and Measuring Tape Factory) in Vác, where mostly prisoners produced the slide rules. From the end of the year 1951, due to restructuring, the company named KÖMI (Directorate of Public Interested Works) Corporation No. 101 continues the production. From 1955, the line was moved to the Brush Factory at Monor, where the production was started on October 1957. These rules has the markings "Logar" instead of "Gamma". Due to application of national standard MSZ 4617-57, the rules was modified: the 10-inch Darmstadt rule has two new markings for converting small angles to radians (and therefore calculating sine or tangent of the angles specified in minutes or seconds), the pocket rules has new standardized typeface in front scales and modified scale names on the back of the slide. Apart from these, they produced these rules to the end of 1970s.

The advantage of these slide rules was the relative low price - compared to western rules. The earlier rules was more precise instruments than these were produced in the 1960s, and 1970s. The pocket calculators and legally imported western slide rules mostly made by german manufacturers were cheaper year by year, so the hungarian-made rules hasn't any chance to survive the decade. (Two russian factories has been produced slide rules to 1991!)

Gamma 2503/2512Try it!

The 10-inch rule type 2503 was planned according to the widely used Darmstadt scale-order, which type was in production from 1949 to the end of 1970s. The rule, and the glued-on celluloid pieces was produced by classic procedures, but the window has been made by plastic instead of aluminium-framed glass used commonly in these days. On the upper side has the standard cm- and the log-scale, in the front there are the cube (K), the square (A, B), the base and inverse scales (C, CI, and D) and the pythagorean (P) scales. On the lower edge has the trig-scales in decimal angular system (Sd and Td). On the back of slide, there are the exponential, or log-log scales (LL1 to LL3). Similar to the professional rules, the scales on which the numbers are decreased from left to right, and the scale-extensions on A, B, C and D scales was printed in red. On the back side, a sheet of paper contains the most important mathematical constants and small drawings demonstrating the use of new scales compared to Rietz system was glued on. There were some variations: on the later Gamma-made pieces, all scales painted in black; the Gamma text was later replaced by Gamma logo.

The rules (and some other tools) produced at the Gamma have been classified at the end of the manufacturing process, so the more precise ones has the stamps "I. osztályú" (first class), the approved others has "II. osztályú" or "II. osztályú szépséghibás" markings in the stock. The price of these rules was Ft 169 (first class), or Ft 113.50 (second class), and supplied with a card-box and a brief instruction.

The Gamma/Logar 2503/2512 slide rule

Gamma 2511Try it!

The 10-inch Rietz rule typ 2511 was in production much less time than others, only manufactured in the Gamma plant. The rule was made of aluminium, the scales in two colors - ordinary scales in black, inverted scale and extensions in red - were painted with white background. The structure is very interesting, has similarities with wooden rules: the upper and lower half of the body were connected by metal sheets. There are more unusual things: the 3-index window made of plastic was framed in 3-direction, and on the frame there is a gamma-sign related to Gamma factory; on the back the rule has two holes make the rear trigonometric scales readable; the slide is trapesoid-like so it can't be inserted inversely. The machines required to produce this type of rule weren't moved to Vác, so the line was closed in 1951.

The Gamma 2511 aluminium slide rule

Gamma 1252Try it!

The other type in continuous production was the model 1252 5-inch pocket rule. This has identical structure as the 10-inch type 2512 - made of pear wood and celluloid with copper reinforcing and steel plate springs. The evolution was the same, too: the earlier pieces have two-color scales, the latters printed in black only; the manufacturer-marking was changed the same way. After the standard MSZ 4617-57 has been applied, the whole template for the front scales were re-designed with standardized letters similar to ISO-script, and the scale names on the back were changed from S, S&T and T to sin, sin&tg and tg, so these rules can be easily recognized.

The Gamma/Logar pocket slide rule

Artillery pocket slide rule

This rule was made for the Hungarian People's Army, and has special sine and tangent scales for solving ballistic calculations in mils (6000 mil = 360°). The rule was almost identical to the type 1252, but the bigger holes on the back haven't indices, so the back scales on the slide can only be used when the slide is inverted.

ROBOT machining slide ruleTry it!

This type of slide rule was specially designed for metal-cutting purposes. Instead of ordinary scales it has special logarithmic scales for setting/reading cutting speed or rpm (v,n), diameter or length (d,h), floor-to-floor time (t), or feed (e). For more common calculations with logarithms, sine and tangent, it has these scales on the back of the slide and the common A-scale on the front for reading the function values. The window has five special indices to easily calculate weights of some materials (V - steel, Al - aluminium, R - copper) with square-, circle-, or hexagonal cross-section. The rules was supplied with more detailed printed manual to help the workers.

The Gamma ROBOT machining slide rule


This instrument is similar to navigational slide rules or computers used by pilots, but in circular format. The háromszögmegoldó (Triangle-solver) is identical to DR-3 (the german Dreieckrechner) type used in Germany in the World War II, except for the hungarian labellings.

Further readings

Slide rules manufactured in Hungary
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