" wrote in
:

Depends. If you are just doing this one job and that is it, then do
as suggested elsewhere and measure twice and cut once. You can clamp
a straight edge to the plywood and cut exactly where you want to cut.
Might have a bit of trouble finding a true straight edge that is 4 or
6 or 8 foot long to guide your saw. This approach requires time to
clamp the straight edge exactly where you need it. Not a slam bang
thank you maam job.

If you want to cut this plywood and lots of other plywood exactly
where you want every time, then get a rail guided track saw. Such as
the Festool TS55 or TS75 saws. Easy to use these saws. Just lay the
guide rail on the pencil marks, clamp in place, run saw on guide rail.
Done. Quick and easy. This is the method to use if you are going to
cut plywood exactly over and over.

I bought a 4' aluminum saw guide from Woodcraft. It takes a bit of
fiddling to get it right, and I have to make sure I measure the offset
correctly as well. Once it's on, it's plenty solid for my purposes.
Most of the time, the fiddling doesn't take more than 5 minutes. For my
purposes, it was $30 well spent. (Plus, as along as I adjust for the
offset, all my portable power saws & routers can use it.)

Puckdropper
--
Make it to fit, don't make it fit.