-49.9% is the change from 511 to 256
Calculation steps:
[( 256 - 511 ) ÷ 511] x 100 = -49.9%
Formula
Percentage change = [(256 - 511) / 511] x 100
Subtract the new number by the original number
256 - 511 = -255
-255 ÷ 511 = -0.49902152641878667
-0.49902152641878667 x 100 = -49.9%