Calculating Machines --- Abacus --- Napier's bones --- Slide Rule --- Logarithms --- Calculator
Nowadays, nearly anyone who wants a machine to do a calculation uses a calculator. These were originally called electronic calculators, to distinguish them from mechanical calculators, or pocket calculators, to distinguish them from computers!
Here is some practice in checking if calculations are reasonable:
You would think that all calculators would work in the same way for simple calculations. In fact, they have their own peculiarities. If you calculate 1 + 2 x 3 on the grey calculator above, it will produce the answer 9. It adds 2 to 1, then multiplies the whole thing by 3. But this isn't the way that mathematicians do calculations. They work out all multiplications and divisions first, then do the additions and subtractions after. So 1 + 2 x 3 gives the same answer as 2 x 3 + 1, which is 7. You will find that the calculator below does this. It has other helpful features. You can add or subtract a percentage (e.g. 150 + 17.5%). You can reverse the sign on the result or take the reciprocal ('one over ...'), which is often useful when doing calculations. You can display the result as a whole number, or to 2 decimal places (both rounded), and indeed switch between these if you want. Finally, the whole entered calculation is displayed at the bottom, so you can check if you entered something wrong. You can even change this calculation, and click on 'Redo calculation' to re-calculate it. In the bottom display, the reciprocal is shown as 'n' and the divide by '/', as the other symbols are not in the normal character set.
Most computers have a calculator as part of their operating system. To find the PC calculator, click on Start, then Programs, then Accessories, then Calculator. Click on View to choose Standard or Scientific. Try 1 + 2 x 3 on each!
Calculators have a special notation if the numbersget too large or too small. They display significant figures and powers of ten. The calculators on this page don't, as they are designed for teaching people how to use a calculator, or for simple use. Use your computer's calculator or your own for more complicated arithmetic.
© Jo Edkins 2007 - Return to Numbers index