We have balanced a fan on the balancing machine and when we test on a static balancing stand, we see heavy spot in the fan. What is the problem?

In the picture above a dynamic balancing machine measures the resultant of the three resultant unbalance forces namely the static component “S “, and the couple component “+C and -C” The values can be recorded by using the program two plane measuring and static/couple measuring sections.
When using a machine you compensate all un balances ie S,+C,-C. But when check on a static balancing stand the couple portion unbalance do not get compensated, and only S is compensated. So you have the high spot settling at the bottom on a static balancing stand for components balanced on a machine. In actual service conditions when the dynamic effect of all three forces are acting the
fans balanced on a machine for both Static and Couple will be smoother.