acceptable misalignment in circular saw plate?

I'm wondering what kind of misalingment in a circular saw base plate is "acceptable".
Mine is a right-blade depth-adjustable (Porter Cable 447K), and at some depth settings the rear of the saw blade is about 1mm closer to the farther (left) edge than the front of the saw. If I try to do anything like this: http://www.womeninwoodworking.com/tips/startingpoints7.cfm then the saw will either track away from the guide or the blade will score the workpiece about 1mm more than I intend to cut. (And the misalignment varies w.r.t. depth as well!)
(The front is 5in from the edge of the kerf dead-on, as touted by the specs.)
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Daniel,
With the blade fully extended, use a square and see if the blade is perpendicular to base, both front and rear. Adjust accordingly and then lower the blade some and recheck. Once satisfied that the blade is staying perpendicular at all blade settings, now you can check the distance from the edge of the base to the blade - front and back. Just a couple of thousandths off can cause the problem you're experiencing when the saw is being referenced against a fence.
I'm not sure about the adjustments on that model so I can't tell you how to do it but the Porter Cable site should have a manual available if you don't.
Here's the link http://media.ptg-online.com/media/pc/Owners%20Manuals/20021115200000_En%20900003%20-%2004-09-02.pdf
Took a quick read and they do not have a procedure for checking or adjusting the blade to base edge for being parallel. Make the measurements as above and if they're off see if there are any screws on the base that can be loosened that would allow the base to be shifted slightly. That's a molded base, maybe the one edge is off?
Bob S.

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Bob,
Thanks for your comments.
The base is not adjustable. I exchanged it and got one which is almost perfectly aligned, only about a paper-thickness worth of difference (maybe 3 thousandths?) along the length, at various depths, in this sample.
- Daniel
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