Hi Phil
Have a great bit of software for quoting, a piece of string pinned to a map on the wall. Not gone wrong in 34 years, (a bit like my planes), although I do remember it breaking some time in the early 80's. Suspect you have a very similar piece of string.
Seriously tho' a well calibrated piece of string can be just as accurate as fancy computer programmes and very much quicker. You can calibrate in time, distance or even £ , very flexible.