"DerbyDad03" wrote

Even the window supplier that I am using suggested that perhaps I
should offer a contractor a small fee to measure the window "on his
way home or if he was in the neighborhood" to make sure I got the
measurements right.

I pretty sure I know what I'm doing. However, this talk of "casements
windows can be tricky" has me second guessing myself.

EXT gave good advice here. There are several measurement points involved,
not just the obvious 'up down, side side'. Depth of fitting and what Mom
told me was 'rill depth' (I do not know if she used right term, am not a
professional window person).

Last time I did this was 1974 and I took the window out, frame and all,
covered opening with plywood, and Mom took me and the window to the store.
Back then, you didn't contract via the internet for a shipped one. I noted
one side had been shimmed with 1/4 inch soft pine, by the removal time
slightly compressed. Evidently a weather expansion/contraction element in
that case? We replicated it with the new one and had no problems in an area
with significant temp shifts from 110F to -5F at the extreme ends.