It is very useful to have simple approximations to the cumulative normal distribution. About every statistician carries a pocket calculator, but how many of us carry a book of tables everywhere we go? When working 'with a desk-top microcomputer it would be inefficient to have to stop to look up tables frequently. One could store a look-up table, but this would use up a lot of storage and the accuracy of interpolation in the table may not be good. The approximation does not have to be all that simple for the micro or programmable calculator but clearly it should be very simple for manual operation of a calculator, and simplicity would also help you to remember the formula. All of the formulae used in this paper were calculated very easily on a Casio 502-P programmable pocket calculator.