What method used to measure irregular solids?

To measure what quantity of irregular solids? If its volume you are referring then you can use the volume displacement method where you need a measuring cylinder, water and possibly a displacement can.

Measure a known quantity of water. Then immerse the irregular solid in this cylinder. The rise in the water level equals the volume of the irregular solid. Note that if the irregular object floats, a sinker must be used to fully immerse the irregular solid, where the volume of the sinker should be known.

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