The Curta.org Bulletin Board

[Peter Johnson]

I acquired my one and only Curta (a grey Model II) a short while ago, and would like to start by thanking everyone who has posted information on the history, care and use of these wonderful machines. The information has been invaluable to me and I'm sure to many others.
My main interest is using the Curta for the purpose for which it was invented - to do calculations, and to this end I have a couple of questions. Firstly, if the need arises, is it OK to turn the clearing lever anti-clockwise, say to clear just the Result Dial? I can see no reason why not, but it's better to be safe than sorry.
Secondly, does anyone have a copy of the cube root tables referred to by Contina in the Computing Examples booklet? I have a picture of the front page, taken from an eBay sale. I understand how they created these tables and could create an equivalent if I had to, but not wishing to re-invent the wheel, and not to mention being of a lazy disposition...
Peter Johnson
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PeteJ

[Pete]

Hi Peter,

The clearing ring can go in either direction, just be sure to raise the carriage before you go spinning it around...snap that spider spring and you'll either be sending it to Jack's Injured Curta Ward or looking at a rather tedious repair using tools very few people have handy.

About cube roots, gad, I've got all the literature...okay, cube roots are pp 14-16 of 'Computing Examples for the Curta Calculating Machine', but...I'm not doing all that typing, hmph. Basically, square roots are calculated by refining an initial estimate you obtain by consulting the thing between your ears, and cube roots are an extension of this. I think these are available on vcalc.net somewhere, have a look at the 'Curta Literature' link there.

By the way, yours isn't a 511xxx is it? I'm always curious about where they changed the slider colours from the earlier to the finalized setup.
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Cheers, Pete

[Peter Johnson]

Hi Pete,

Thanks for the quick response. No, my machine is number 534282, and the sliders go in sequence two black, one red. They are rectangular in shape, about 6 x 2 mm.
I have a copy of 'Computing Examples for the Curta Calculating Machine'. You will see on page 14, they write 'CURTA users who have at their disposal our CURTA tables may, by use of these tables, obtain a cube root correct to 5 figures by means of an addition and one subsequent multiplication'. These are the tables I am looking for. You will see that they go on to describe a method starting with an estimated value, and this calculation is repeated until sufficient accuracy is achieved. My next statement is something of a simplification, but what the tables do is to give a set of estimates, and the selection of the appropriate value is guaranteed to give 5-figure accuracy with only a single calculation. I can explain where their formula comes from, should anyone be interested.

Peter Johnson
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PeteJ

[Pete]

Whoops, pp 52-54 of the 'Mathematical Handbook, An Aid to Every Day Figuring Problems, Tables, Formulas, Arithmetical Rules'? Gives 'em for 0<n<100, anyway.
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Cheers, Pete

[Peter Johnson]

Pete-

I can trump that! The Handbook of Mathematical Tables and Formulas by Richard Stevens Burington gives cube roots to seven significant figures for the numbers 1-1000. However, in both cases we only have integer (whole number) values.
I don't like to be beaten, so I'll press on and create an equivalent table.
Unusually for Easter, the sun is shining here in East Yorkshire. I hope that you enjoy the same weather.
Regards,
Peter Johnson
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PeteJ

[Pete]