Calculators in the 50s and 60s

In the 50s and the 60s, the most widely available and used calculator was the brain, paper and pen. I do remember using plus adder machines which had rows of 0 to 5 numbered buttons on the top; does it go without saying that the buttons were mechanical, not electronic? These machines had but one function – to add numbers; the rows represented single, tens, hundreds etc and the addition of a number was done simply by pressing the appropriate key/button . . .but what of numbers over 5 you may ask – simple, for 9, hit the 5 and then the 4.  The result of the addition was shown on a mechanical numeric display. One had to be certain of what one was doing as there was no way of checking whether or not any number had been entered – for that you needed the even bulkier add listing type of machine where rows of keys, this time from 0 to 9, allowed the entry of a number to be shown on a roll of paper once the big lever on the side had been pulled – I think these machines allowed subtraction as well as addition. No, these machines did not fit into your pocket or indeed into a briefcase but, if you were going on an audit, you did usually pop one into the boot of your car. Because the brain was more often used, many people were able to do what would not be viewed as incredible things; remember that, in the 50s and 60s there were pounds (£) shillings (s) and pence (d) (12 pence to a shilling, 20 shillings to a £) but even so, it was not unusual for people to add columns of £ s d at the same time – just running their eye down a column and throwing a total at the end.