Some of you may have noticed my original attempt to test whether the sledge cut square, using a charlatans version of the five cut technique, and the miraculous 0.02mm error, which in itself was incorrect. I guess I was surprised but considering I rushed to film the process, and forgotten half the procedure it is not surprising.
So I decided to re watch NG's detailed and instructive video about the correct procedure to measure the sledges accuracy. The original video is linked here: http://youtu.be/UbG-n--LFgQ which I really do recommend.
Subtracting the thickness measurement of the top by the bottom, of the slice created from the fifth cut, divided by 4 which is the amplification of error in rotating the piece around. Then divided by the length of the cut and multiplied by the length of the fence gave me -0.4675mm, which is how off the fence is.
27.89 -- 29.25 = -1.36
-1.36 / 4= -0.34
-0.34 / 400 = -0.00085
-0.00085 * 550 = -0.4675 which is half a mm.
And because it is a negative number this means my fence is too low on the side I was cutting on.
Anyway this is just further reason why I should just buy a real table saw.