Strange Method Of Tramming A Mill Vise

[Highpower]

I have a 4" and 6" vice for my mill. Both are keyed. I lucked out with the 6" vice in that all I have to do is tap it to one side while tightening the mounting nuts and it comes out spot on every time. One problem though was that I always forgot which DIRECTION to tap on the vice. With my CRS disease I finally resorted to simply drawing a couple of arrows on the front of the vice to remind me.  

But the 4" is a different story. "Spot on" is floating somewhere in the middle of the slight clearance on the keys. I tried Tom's method right after he posted it and was blown away by it. Got it perfectly trammed indicated on the first try. I'm still thinking about trying to switch the keys around on that one though, or getting a different pair of keys to see if I can find that magic spot where the vice is spot on when it's tapped all the way to one side. Such is life for those of us who DON'T have a surface grinder.