Во избежание ошибок... (To avoid mistakes...)

Written on a brass label, right next to the crank-handle:

Во избежание ошибок, 

начан оборот, 

добыл ручку до kонца.

With the wonders of the information age and the internet, this label can be read approximately as:

To avoid mistakes, 

when turning started, 

get the handle to the end.

This makes clear - the calculator does not have the protection against reversing direction half-way through a turn. Doing so would indeed mess-up the results of a calculation, so an instruction to complete a turn when started.

This is a relatively early Feliks (Феликс) calculator, model A3 and was made in Moscow probably around 1930. As is well-documented, a few years after the revolution of 1917 the Odhner factory in St. Petersburg was dismantled and moved to Moscow. From the early 1920s (?) the Arithmometer continued to be made there, in the late 1920s new models A2 and A3 were introduced. From about 1928 the machines were made by the "state plant of calculating machines named after Comrade Dzerzhinsky" and were labeled "Feliks".

This machine has serial number 52284. Whilst there isn't much clear serial number data for the machines produced by the factory in that period, from its features and labelling it most likely dates to the 1928 - 1932 range.

Around 1931/33 (?) an updated model was introduced with the characteristic 'corner-feet' baseplate. This basic Feliks-model was then manufactured for decades. After the Moscow factory was closed in 1941 and moved, manufacture of the Feliks starts again in the Kursk Calculator Factory in the late 1940s to continue well into the 1970s.

This A3 still has many of the recognisable design features of the original Arithmometer, it still is very much an Odhner Arithmometer. Although simplified, the drum is also still made of brass and steel. (Later designs replace brass with cheaper zinc-alloy and have a general further lowering of build-quality.) The mechanism is basic, functional - without much in the way of interlocks or safety.

The calculator feels fairly 'rough', with large tolerances on movements. (Compared to the heavy precision of a contemporary Brunsviga Nova, it feels positively shoddy.) Despite that, it does work and is a useful calculator. Its 'build' requires a bit more care from the operator perhaps, but will have made it much easier to manufacture and to maintain the calculator. 

The calculator has quick clearing; a sliding bar under the front of the top-cover can be slid sideways to block the slots and a quarter-turn of the crank then pushes all levers back to zero. On Odhner machines this quick-clearing disables the full-turn safety to enable the quarter-turn-and-back. The Russian machine solves this problem by simply leaving out this safety completely. Hence the extra warning label instead.

The labeling on the calculator gives extensive information on its source.

мснх   рсфср 

трест тoчной пеханиыи

гос. завод счетных mашин

им. тов.  Дзержинсного

москва

The мснх means the Moscow Soviet for National Economy and the рсфср is Russian Soviet Federative Socialist Republic. Then; 

trust for precision equipment

state factory of calculating machines

named after comrade Dzerzhinsky

Moscow

With Феликс as a 'brand'.

Apart from cleaning the machine, the detents for the carry-levers needed to be repaired. The small springs that hold the carry-trigger levers were broken on several columns - this caused the machine to make errors especially in subtraction. Removing the carriage is fairly straightforward, once the left side-cover of the carriage is unscrewed and rotated to allow the carriage to pass the counter-finger!

Then the rod that holds all the star-wheels for the result-register can be withdrawn, releasing all the carry-levers.

The carry-levers are held in position by a detent that is a small rod, spring-loaded in the lever. This chisel-ended rod pushes against the rod that holds the star-wheels.

In keeping with the general 'carelessness' of this machine, the spring-ends are not closed and merely consist of cut lengths of spring. Several of these had broken (inferior quality?) and the two ends wound into each other. In operation this caused the lever to be pushed back by the carry-pin before performing a carry - thus leading to errors. 

Fixed by separating and closing the ends of any broken springs and then all re-mounted. After this repair, calculating 525 - 7 again gives 518 instead of 528.

New 3D-printed rubber feet were fitted and one missing screw added to mount the bottom plate. This bottom plate is a bad fit, askew the base-plate. This is because the holes in the plate are stamped off, as if the plate was not placed properly in the stamping tool. It could be rectified by filing the holes larger, but was left as is - in keeping with the general character of this old Soviet-made calculator (i.e. its apparent 'careless' build-quality).

The Feliks clearly shows shared Odhner Arithmometer design-origins with the Swedish-made Original Odhner calculators. Compared to these Swedish calculators the Feliks hasn't developed much from the Arithmometer design near the end of Odhner in St Petersburg - in fact it probably regressed a bit. And then from the late 1930s it stayed essentially unchanged until the end of production in the 1970s. It even kept the by-then decidedly quaint wing-nuts until the very end of production.

When seen side-by-side with a 1930s Swedish-made Odhner, the overall difference in build-style is noticeable - on the Feliks it all works but there is just a general 'roughness' about the machine.

Now cleaned, preserved and operational again - avoiding mistakes :)