Adjusting for height is easy. You can even scribe arches up to 16 feet wide.
Laying out a segmental arch across
an opening can be time-consuming
if you don't already know the radius or
have a fixed point to work from. You
could calculate it from the height of
the arch and the width of the opening,
but that's not the kind of math most
carpenters remember off the top of
their head, and the trial-and-error
method can be costly.
If you find yourself needing to lay
out these arches from time to time, or
if you would like to, you might want to
take a look at the E-Z Arch
(E-Z Components, 3838 Raymert