Thanks for the video, I already use that method as I find it more accurate than a square, if you cut a 1/4" deep line in the block of wood the blade has to fit in the slot when it's reversed. If it doesnt fit it's not 90 deg to the table. I did it with an engineers square and I thought it was perfect, but after double checking with the wood method I found I was about 1 1/2 deg out.