I set it pick a number between 2 and 217 for the page - 30
then either A to E or F to K - represented by 1 to 5 - 2 or B/G
finally a number between 1 and 7 for the other coordinate - 2
I was given page 30, B2 which looks like this:
It's an area just south of elstree in NW London, about 17 and half miles out from central london.
Weather permitting, then, I will cycle there tomorrow. It should entail a 65 mile ride in total, which will be very good for my stats.