The ones I've used seemed so broad, trimming really didn't
seem to be needed. It's kind of like using a matching device
with a mobile antenna. For most, it will be left at a single
setting, even for a whole band, and any tweaking done will be
at the antenna. I'll usually cut one to the usual length and
throw it up. IE: for 40m, I just cut 22 feet and I'm usually
done with it. They don't seem that critical.
I have an old puter program that would calculate those for most
any situation, but it must be on one of the drives I'm not using
at the moment.