Save time driving on the streets of London with this short program from David Lewis

The program presented here, London, prints out the shortest route between any two points in Greater London.

It is used in conjunction with the Geographers' Master Atlas of Greater London, which covers an area of more than 2,000 square miles bounded by Potters Bar, Grays, Coulsdon and Windsor.

The map references for the squares of origin and of destination are entered as an eight-digit code, e.g. 27K247J1 (Southgate to Heathrow Airport. Ignore page numbers, and if there is no index number after the letter in the map reference use zero.

You may also enter the description of address of origin and destination, which will then be printed out, or you may instead enter Return. London will print out the approximate distance in miles and kilometres between the two points. It will then print the map references for each square of the Atlas (including those for both points) through which you should pass when taking the shortest route.

It is then a relatively simple task to plan your car journey, using the Atlas. The effect is as if you had the pages of the Atlas pinned on the wall as a composite chart measuring some seven feet by eleven feet, for planning the straightest route with map pins and cotton.

If you have a cassette player in the car, it can sometimes save time over a long, unfamiliar journey to record the details of the route and play the tape as you go along.