Plural of coplanarity; multiple instances or measurements of the quality of being coplanar.
From 'coplanar' plus the suffix '-ity' (creating an abstract noun) plus '-ies' (plural suffix), following standard English nominalization patterns.
Engineers and manufacturers measure coplanarities with lasers and precision instruments because even microscopic deviations cause problems—a perfectly flat surface that's off by 0.01mm can ruin an entire assembly.
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