Balance actually describes the imbalance of the result. The number displayed is defined as the maximum difference of each thread over multiple runs, :
Balance is an indicator of the health of the result. Specifically, runs with a balance number of should always be repeated.
High balance numbers can also be indicators for unbalanced workloads, where one core is doing significantly more work than another.
The balance number can be improved by reducing the difference in workload between different cores. If the current workload is very small, increasing the workload might also help.