You started from a known position and you arrived at a place the position of which is at present unknown.

We shall fix the position of that spot by applying two factors, the distance that you travelled and the direction in which you were moving.

The direction is given by the compass; and, as the horse seems to have kept up a remarkably even pace, we can take time as representing distance.

You seem to have been travelling at about eight miles an hour, that is, roughly, a seventh of a mile in one minute.

So if, on our chart, we take one inch as representing one minute, we shall be working with a scale of about seven inches to the mile." "That doesn't sound very exact as to distance," I objected.
"It isn't.