On 4 March 2015 at 03:01, John Ferrell wrote: > Adding machines have not always had a minus key. To subtract the > operator would "9 it out". > Suddenly I feel old and tired... > > Uphill to school both ways in the snow with bare feet in a cardboard box at the bottom of a lake ... :-). Shortly after the HP35 was released Casio released a more affordable 4 function calculator. Only about $100 in 1973 dollars AFAIR against the HP35's $465 (if my memory serves at this remove). A friend bought one and I bought it from him a year or few later when he upgraded to an HP45. It did have a minus key. BUT no decimal point. There were 8+8 digits afair in two "banks".. You pressed a shift button to see the lower 8 digits in a result. If you eg performed 1/3 the top bank showed 00000000 and the lower bank 33333333 as you'd expect. So far so good. However, only the upper bank was used in subsequent calculations. So eg 1/3*3 gave 00000000 00000000 To maximise significant digits and fodder for the next calculation you had to right pad with zeros while ensuring that the result was never so large that it overflowed. Instant death for that calculation. So eg 10000000 / 3 =3D 03333333 33333333 x 3 =3D 09999999 00000000 Good enough. For multi part calculations the occasional 0's were added to keep the active digits in play. Needless to say, keeping track of the decimal point position was a challenge. The initial purchase was made in the final year of our engineering degrees. Our Professor (A G Bogle) was scathing - he said that the only advantage of a calculator over a slide rule was that the former kept track of the decimal point for you - and that this one did not even do that. Despite this alleged lack of capability the (decimal) pointless 4 function Casio was always the centre of a scrum of would be engineers queuing to use it. Russell McMahon On 3/2/2015 1:59 PM, James Newton wrote: > > > "Subtracting is NOT adding plus a bit." > > > > (one of my very favorite double entendres) > > > > This was my attempt to explain it (see "Advanced" and the comment on th= e > > bottom) > > http://techref.massmind.org/techref/logic/sub5.htm > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .