The natural 'stiction' in the suspension system will always render results variable - as James suggests that can be overcome by replacing the spring/damper units with solid rods. However, when you put the shocks back on that will alter the results again.
If you use four mini-scales, then it will tell you your front/rear weight distribution. If you need to balance the car side to side, then use some balance buttons not the scales. Use the 'lifting' method front and rear to make sure the shocks are equal length.
If you are going to use corner-weight scales, then go by the maxim that setting up this way is a matter of being roughly right, and not precisely wrong. HTH
