Are you following Paul Sellers Woodworking Masterclasses, like me?
He is building a Shaker Style Stool (or bench) with sliding dovetails.
For making the sliding dovetails he is using a jig which is simply a piece of wood with an angled edge.
The question came up how to establish that angle to the block of wood with hand tools only and being precise.
Here is how I would do it....