Madas 20BTG, as its sister 20BTZG, is considered as the culminating point of development concerning the calculators made by the firm Egli. It was also the most expensive one (four times the price of a 16eN, for example). An additional register is fitted to this model. This is an “Accumulator Product Register”, generally named “Register IV”. It can be cleared only by means of a “thumb-lever” to its immediate right. Whereas, normally, “Register I” clears automatically before the formation of each new product, “Register IV”, as its name implies, accumulates successive products. It may be disconnected by moving the lever situated on the machine-casing to the left of “Register III”.
A black lever situated to the right of “Register I and II” allows choosing if a number added into “Register I” is added to, or subtracted from “Register IV”. In this way, for example, by using this control, it is possible, while forming positive individual products in “Register I”, to accumulate them negatively in “Register IV” or vice versa. This carriage, named “Triplex”, is more complex than on other models. Several hundred of manufactured pieces have to be assembled. Removing and refitting the Triplex carriage is a rather tricky task, as we can see with the presentation, explained in detail by John Wolff, on its John Wolff’s Web Museum.
Model 20BTG is provided with a second Counting Register to the left of the first (yellow figures). While quotients, for instance, can be accumulated in the right-hand Counting Register, this second register clears automatically after each individual division. There is no tens-carry in this Register. See the difference with Model 20BTZG.
To accumulate quotients in Register II, a small knob to the immediate right of Register I must be turned with its groove vertical. With the screw in this position it is impossible to clear the Register.
Photos below show that two different versions of the keyboard exist, one with all keys of the same colour, one alternating green keys with white keys.
The motor of the 20BTG is pretty similar to the 20BTZG’s.
