MSZ 4617 - The hungarian standard for slide rules

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Brief description

The first revision of national standard for slide rules published in 1957, the specifications described in that would be obligatory from 1 August 1958. The second revision which was only differs in few points was published in 1969 and became compulsory on 1 July 1970. The standard was cancelled in 1980, after closing down the slide rule producing line at Brush Factory of Monor.

The standard describes six kinds of rule, these were produced or planned to produce in these days.

• 125 mm (5 inch) school slide rule
• 125 mm (5 inch) general slide rule
• 250 mm (10 inch) general slide rule
• 250 mm (10 inch) machining slide rule
• 250 mm (10 inch) electric slide rule
• 500 mm (20 inch) general slide rule

The slide rules must be made of wood (steamed pear or walnut) and plastic, plastic, or light alloy. The window must be made of glass or plastic framed with aluminium.

The technical specifications are differs according to the defined two precision class which classification must be stamped on the rules and on their cases too.

On the back of rules of all types except the pocket sized ones must be glued on a chart with often used equations and constants.

The standard describes the minimum required scales for all types:

• the 125 mm school slide rule is a simplified wooden rule, which body is made of one piece of wood, and must contains the A, B, C, D scales and the mm-ruler. The constant "c" must be signed on the A and C scales. The window must have only one index.
• the 125 mm general slide rule body is made of two pieces of wood with brass reinforcing connected with steel springs, and must contain the A, B, C, CI, D, K, L, S, ST, T scales and mm-ruler. The window must have 3 indices, the left for the constant c, the right for converting kilowatts to HPs.
• the 250 mm general slide rule is the same as the 125 mm version, but with A, B, C, CI, D, K, L, LL1, LL2, LL3, P, Sd, Td scales and the mm-ruler.
• the 250 mm electric slide rule has the same construction as the other 250 mm types, but with A, B, C, CI, D, L, LL1, LL2, LL3, Sd, Td and the voltage drop (V), and dynamo-/motor-efficiency (n) scales, and mm-ruler.
• the 250 mm machining slide rule has the same construction as the others, but has special scales designed for cutting time, revolutions, cutting speeds etc. with markings used on the Robot slide rules manufactured by Gamma. Its window has five additional indices according to relative density of aluminium, brass and steel, and for calculating weight for these materials with circle- and hexagonal cross-sections.
• the 500 mm general slide rule is the same as the 250 mm general slide rule except its size.

The standard has specifications for constructing all the scales: divisions, numberings, extensions, constants and which scales must be labelled.

The two precision class are differs in these manners:

• weight of division lines
• divergence of division lines from the nominal values
• difference between surfaces of the slide and the body
• gap between the body and the slide
• distance between lower surface of the window and the upper surface of the body
• divergence of body from flat surface

The standard describes the method for calculating places of divisions, but does not contains the required equations for calculating special scales (e. g. the cutting speed-scale on the machining slide rule) Apart from that, the slide rules approved to the standard are:

• the 125 mm school rule is a deviation of the pocket-size Gamma-made general slide rule,
• the 125 mm general slide rule is a Rietz rule, and identical to the Gamma-made model*,
• the 250 mm and 500 mm general rules are Darmstadt types, and identical to the Gamma models*,
• the 250 mm machining slide rule is identical to the Gamma-made Robot slide rule,
• the 250 mm electric rule is a variation of the Gamma-type general rule which has two additional scales on the front (as found on Faber-Castell's /78 and /98 models).

The hungarian-made slide rules and its conformity

In the publication of the first revision (1957) slide rules were not produced in Hungary, the Brush Factory in Monor was setting up the production line. The rules conforms to the standard showed the following differences than older pieces:

• the edges of the body and the slide must be rounded off
• the glued surfaces must be deeply nicked due to technological reasons and extended durability
• have modified labellings (on the pocket rules the S, T, S & T were replaced to sin, tg, sin & tg)
• the 250 mm rules have additional markings for converting small angles to radians and calculating sine and tangent for these angles

It's interesting to note that pocket rules have markings for standard MSZ 4617-57, does not conforms to all specifications:

• the scale L should be marked with "lg" label,
• the window should be made with same indices as the 250 mm rules have.

The second revision (1969) did not alter the previous specifications, but contains possible modifications for slide rules, which have folded (CF, DF) scales instead of normal scales (C, D). Such rules haven't ever been manufactured in Hungary.

Further readings

Slide rules manufactured in Hungary