larry is correct. if you balance the wheel by first only placing one weight on the wheel, you will have an improper balance.

by using only one weight on one side you effectively change the location of the heavy spot on the tire assembly. that machine doesnt know that you are planning to use the weight on the other side after another spin. it simply asseses the imbalance of each spin and reports.
we calibrate our balancer every morning, and usually after balancing a truck with heavy wheels too.

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'O=00=O'
bmw 2002.
long live the legend