-21.05% is the change from 646 to 510
Calculation steps:
[( 510 - 646 ) ÷ 646] x 100 = -21.05%
Formula
Percentage change = [(510 - 646) / 646] x 100
Subtract the new number by the original number
510 - 646 = -136
-136 ÷ 646 = -0.21052631578947367
-0.21052631578947367 x 100 = -21.05%