Snap Influence

Does anybody know of a way to increase the default snapping "influence" (I can't think of a better word to describe it! ).

The issue is with my sloppy old mouse. It seems to wiggle sometimes a bit, just a couple of pixels here and there. So, while working on CAD, if I chose the Polar Tracking option to make a straight line, it wiggles and hence looses the "grip". The only way left, then, is to go for the Ortho Mode ...which is ok, but not what I need as it is too constrained.

So, is there a setting or a system variable that controls this snapping influence sothat I can increase it...

Just to make myself clear, I am refering to this distance between the line and the cursor here:

Try increasing the Aperture size. Type Aperture at the command line, and you can go up to 50 pixels wide.

Beautiful! ...just what I needed. Thanks mate.

--Edit--

I wonder why have they kept the shape of the pickbox and aperture (even the grips) as a square, rather than a circle, which in my opinion would have been more logical! ...just a thought.