alan_m wrote:

I measured the opening, marked up the trim and
offered up the trim to the opening before cutting. It's the correct
length but I cut both mitres in the same direction!!!
It's at that point you think "phew, good job I've got just enough spare
to cut another length from" and you cut the mitre in the other
direction, then realise you should have cut it in the *other* other
direction!