The scale is designed with the assumption that the load will be parallel to the direction of gravity and perpendicular to the weighing platform; basically, there is only a vertical force. An uneven balance or scale causes the introduction of a horizontal force which affects the weight reading. The general rule of thumb is that if it’s an industrial application such as a floor scale, as long as all of the feet are touching the ground, the results will be within tolerance. For laboratories, however, and customers who want more than a general “rule of thumb” response there is actually a procedure for determining the exact effect the slope will have on the measurement.

Read more about the effect of slope on accurate weighing here.