This is a simple project that can be very useful, build one now and save some time !
Step 1: Cutting the Mdf
Start by using a circular saw or a mitre saw to square the edge.
Then cut a narrow strip.
Adjust the mitre saw to 45* then cut a right angle triangle be sure that at least one edge of the mdf board is a factory edge
Step 2: Glue Up
Clamp a try square as shown in the picture then glue the strip to the edge of the square.
Apply clamps ensuring that the strip is up against the square hardwood could also be used for the strip.
Step 3: Result + Testing
After cleaning the glue squeeze out with a utility knife your speed square is now ready
you can test the accuracy by marking two lines on a board with parallel edges as shown in the video.