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If you have 3 microtubes, you could create 3 balance tubes and situate the 3 pairs across from one another. Alternately, balance the centrifuge without using balance tubes by positioning the 3 microtubes at 2 o'clock, 6 o'clock, and 10 o'clock. The clock positions work well when balancing a 12-hole centrifuge. Other common sizes include centrifuges with 24 and 30 holes. To balance the centrifuge using 5 microtubes, first fill 1 balance tube with water. Then position 3 tubes at 11, 12, and 1 o'clock. Position the other 3 tubes at 5, 6, and 7 o'clock. The balance tube can be located in any of these positions. Balance the centrifuge with 6 microtubes using the same configuration, but swap out the balance tube for a sample-filled microtube. Place 2 sets of 4 microtubes in a way that the sets will counterbalance one another and center the weight in the centrifuge. Place 4 microtubes (including the balance tube) at 11, 12, 1, and 2 o'clock. Then place 4 more microtubes at 5, 6, 7, and 8 o'clock. You can balance a centrifuge using 8 microtubes in the same configuration. Just replace one of the microtubes with a sample-filled tube.
Balance 3 microtubes by placing tubes at even intervals. Position 5 microtubes with 1 balance tube. Situate 7 microtubes and 1 balance tube in the centrifuge.