The side pieces of the mast are rebated on both edges to accept the front and rear pieces, creating a box section.
Here the rebate has been marked up on the face of a side piece.
The rebate on the face is 3/4" wide, which is the thickness of the front and rear pieces.
In this pic I have used a cutting gauge to mark up the rebate on the edge of the side piece. This rebate is 3/8" deep.
The cutting gauge enabled me to make a line exactly in the centre of each edge. I then ran a pencil along the cut to make it visible.
I will be setting the circular saw to cut to the required width and depth when making the rebates, so will not be cutting freehand to the lines. The lines however will give visible confirmation that the rebates are being accurately cut.
Here is a side piece in the vice marked up and ready for cutting.
The mast is certainly a time consuming project!