-50.49% is the change from 515 to 255
Calculation steps:
[( 255 - 515 ) ÷ 515] x 100 = -50.49%
Formula
Percentage change = [(255 - 515) / 515] x 100
Subtract the new number by the original number
255 - 515 = -260
-260 ÷ 515 = -0.5048543689320388
-0.5048543689320388 x 100 = -50.49%