This is built with a relatively cheap Contractor's Square and an angle block I got at an auction for a dollar...
I drilled holes in the square so it would bolt to the block. The block is pretty heavy so it keeps the square pretty solid while in use. It can also be clamped to the table if needed.
Here it is being used to set the height on some Upper Control Arm Mounting brackets.
Being that it is aligned with the edge of the block it is very easy to set up square dimensions from layout lines on the chassis table.
If I need an EXACT set up height I use my engineering scale to layout the exact dimension. I will scribe the height and lay in some red or yellow marker to highlight it.
Thanks for looking.