Corner balancing, how to ensure level

I bought the wireless corner scale set that was linked on facebook.  How do i setup my driveway level?  I vaguely remember coming across a method using water, buckets, and cheap vinyl floor tiles from lowes.

Any thoughts?

Cheap laser levels are now under $20, and fit in your glovebox. I can't imagine why anyone would want to screw around with water levels for something as small as corner weighing. 

I used a length of square tubing with a digital level on it, and measure front-back, side-side, and diagonals, to make sure it was level.  Shimming with whatever I had that would work.

Went with an 8ft ibeam level for wood working.  I'll start playing with in a weekend or two.

Thanks

When I do this I make sure the car is level side to side but I'm not going to make that big an effort to make it level front to back if the difference is less then an inch.

Of course if i'm setting up a small light car or a formula car with 4 wheel IRS then I may make that effort.  But for my race car which has a beam rear axle I just try to get close on the front to back levelness.