Printed at the foot of the table of hundreds it says:-
The scale of miles goeth rounde about the Mapp
All four map borders are chequered to show miles,
west-east and north-south; the origin of the scales is
top left. Each two miles is labelled across top and bottom,
2, 4, 6, ... 48. The labelling on the sides runs down
a, b, c, ... x (no 'i' or 'u'). Besides being scale lines
the scales and the grid printed across the map in fine
lines make an index grid. John Norden's provision of an
index grid is an innovation in map making.
The scale can be estimated from the scale line
wrongly assuming it is a scale of modern statute miles.
A better figure for the scale has been estimated from
the positions of towns. This also provides a value of the
'old english mile' used in John Norden's scale line.
The process is described in notes DISTTAB.rul
accompanying software which does the sums. The map scale
is about 1 to 241379, say:-
1 to 240000
John Norden used an:-
4 miles to 1 inch
old english mile = 1.24 statute miles