I've never worked the Mason Dixon mitered square (I have to book I should try it out). I think MD's mitered square instructions seem so different because they are using stockinette stitch, not garter stitch. Garter stitch is more 'square' then stockinette, so they throw in extra decreases to square it up more.
Mirl56 at Ravelry, too.
Learn from the mistakes of others. You canít live long enough to make them all yourself. Eleanor Roosevelt
Lady Feb Sweater
more shawlettes, socks