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This is relatively obvious method, which I found not used by most of the researchers. Usually the equilibration of 2,3,4,6,8,9, and 10 tubes in 12x rotor of table top centrifuge is simple, but for 5 or 7 most of the people I know use an additional tube. This is not necessary. If you look at the figure provided here, you'll see that 5 is a combination of equilibrated 3 (red) and equilibrated 2 (green or blue). In this situation the rotor is equilibrated. Add two more tubers for 7.
For any other rotor type you can use the same approach. For odd numbers you have to equilibrate 3 tubes first and then always add equilibrated pairs of tubes.