Upon closer inspection: mine is slightly different from yours. The big knob goes in one simple centered hole, only. Otherwise same. Same too is the error, or v close to it. I measure .20 to .25 off. It varies from top to bottom because (ta-dahh) the face of the jig is cupped! High points are definitely the top & bottom edges. Now if the face were square to the base and the piece were longer than the jig is tall, that wooden matter. But, alas...dusty wrote:Yes, it is reasonable to expect it to be square to the table when setting in the miter slot. I just checked mine using the Wixey. After zeroing the Wixey on the table top, the Tenon Master measures .3°.
Using this, without correction, would introduce approximately a 1/64" error at the top of a 2" tenon. For my work, this would be acceptable. ...
Do tenons need to be precise? How precise are your mortises? Honest questions - not sarcasm.
I do hear ya though, on the 1/64" thing. The error is not big enough to make a difference, so I am ignoring it. I've used it a good deal and never had a problem, or never noticed one, anaway.
Do tenons need precise? Nah. Not that precise. And to take it a little further, I'll give SS credit for clever: the square-error is such that your cut tenon will be fatter (microscopically) at the shoulders. So this could be a good thing.
Still just a wee bit disappointed, though, that I don't have a 5 pound rock solid piece of perfectly square cast aluminum for a reference tool.