The 2 min boat tool
If you dont know about this boat building aid here it is
just use a flat piece of wood jointed square, and cut the hole on a bandsaw,
a jigsaw works but make sure the cut is square and true
a jigsaw works but make sure the cut is square and true
and use it like this
use it for cutting the ply sheeting and it also helps for marking to plane the progressive bevels on the stringers