The message
from Roger contains these words:

Leaving aside the inherent lack of precision in subdividing a field into
building plots it is impossible to scale off even as large a scale as
1:1250 to the required accuracy when the thickness of a line may amount
to a couple of feet.

We're lucky - ours is a terrace, so the midpoint of the dividing wall
extended to the midpoint of the back of the garage would be simple.

--
Skipweasel
Pay no attention to that man behind the curtain.