Cutting accurate dovetail joints can be done by making a simple jig from scrap wood from your shop’s cut bin. After you make the simple jig and cut the tapered slug out of the middle, you definitely save it, as you see, the wedge helps keep your saw blade precisely straight and true.
I cover the top and the wide back with self-sticking sand paper for ease of grip. I’ve removed my other hand from holding the wedge in place strictly for this photograph, I find that treating the sides of the wedge with a slick wax or a silicone spray helps to keep the saw moving while you lightly pressure the block.
Don’t become a Gadget-Gary and go buy a plastic jig from a catalog, show yourself you’re a woodworker and you can fashion a functional jig quite easily!