Here are the two squares I use the most in my shop, a speed square and a mini machinist square. I thought I would combine the two and that's how I came up with the idea for a mini speed square.
To make the square I cut a piece of maple to a thickness of 1/4 inch.
This can be used for the triangle and the lip.
I made a few of these so I used different types of wood. To cut the triangle I used my table saw sled and my speed square. I just held the piece firmly and cut a few triangles.
For the lip for the square I cut small strips 2 1/2" in length. I then glued them to the triangle.
Although it was not necessary I wanted to add a triangle in the middle, this can be used for sliding the square along a piece of wood and produce a straight line parallel to the edge. The inner triangle is 1/4 inch and 1/2 inch from the edge.
I drilled three holes and then carefully chiseled out a triangle in the middle of the piece.
Here I am testing the square for accuracy.
The square can be used as a guide for a jigsaw, the saw will cut accurately 90 deg and 45 deg as I show in the video.