> But by the tenets of Linear Algebra, spanning vectors, etc., 
> there has to be. You still have two axes, that's not enough 
> to describe a 3-dimensional space.

But the axis are not aligned exactly with X, Y, Z. Each sensor is on an axis
that has some X, some Y and some Z component to it. And the two sensors have
different amounts of X, Y, and Z between them. E.g. if sensor 1 has 45'X,
45'Y, 45'Z and sensor 2 has -45'X, -45Y, -45Z then there is no way that
motion in some direction could NOT produce a signal.

---
James.
 

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