Runout vs. Flatness and Dial test indicators

Andrew wrote... edge of the Yup, they say to make sure it is in the outer 1/4 inch of the media surface. However, they also specify to make sure it is not on the "extreme edge" or what I mean is, it must be in from the chamfered area. The picture doesn't quite do it justice :) Sure, there's never going to be any data there, but I would worry about microscopic particles coming off the platter where the ball rests (the media is coated to the very edge, no uncoated area visible) and flying particles of oxide are definitely not a good thing. But, it appears that is ok for this operation, and the way they specify to do it. Just to the left of the heads actually, mirror image from the card cage. Yeah, now see, that's the part I can't figure out. Exactly what does that switch accomplish? I know one position is for measuring runout and one for flatness, but what does it actually cause to happen? The lever tony refers to is the joint in the guage, what I was referring to is this "switch" on the guage. Could it be that the older dial indicator wasn't auto reversing while newer ones are, hence, the switch? More specifically, I'm sure I'll never find the original HP dial indicator and holder bracket. So, I'm hoping to use "any old" dial test indicator (I know these terms aren't interchangeable). Harbor freight has a cheap one. The trick is the mounting bracket. As long as the dial indicator from harbor freight could be attached to the drive in a stationary way, I would think it would work for either test and that the HP dial indicator wasn't a "special" one. So Andrew, any idea why the dial test indicator on harbor freights website wouldn't work or easily be made to work? Thanks much!! Jay