The photo shows a combination square and level from the time of Pharaoh Ramses (about 2,000 years B.C.). I could not get to the exhibit, so I bought a glossy photo book, and this page was in the book. The level is a plumb line with a mark on the crossmember of the square. I always wanted to build one of these.
Step 1: Rip three pieces
Wood always moves with changes in humidity. Egypt is a very dry climate, so precision instruments from wood might work there. I made my Egyptian square and level from 1/2 inch plywood because it will not shift with changes in humidity.
I ripped three pieces 2 1/4 inches wide. I made the legs of my square 20 inches long each. The original in the museum exhibit has legs about 14 1/2 inches long.
Step 2: Rough layout of the pieces
It would be possible to build this without the use of a modern square, but I will use one in this step to speed things along. The crossmember will need to be cut to length. Pieces will need to be marked for dado operations to prepare for making lap joints that will be strong after gluing. The crossmember is 2 1/4 inches above the bottom ends of the square's legs. The ends of the square legs need to be cut at 45 degrees so they rest flat on the work surface. If I were to do it again, I would change the crossmember to be more like 4 inches above the work surface along the lines of the original from the museum exhibition. See the photo in the Introduction.
Step 3: Fit the pieces for gluing
Fitting the pieces after cutting them to length and making dado cuts for lap joints should be straightforward, but there can be fitting problems. Make whatever corrections are necessary for a good fit. Glue the pieces at the lap joints.