-23.01% is the change from 830 to 639
Calculation steps:
[( 639 - 830 ) ÷ 830] x 100 = -23.01%
Formula
Percentage change = [(639 - 830) / 830] x 100
Subtract the new number by the original number
639 - 830 = -191
-191 ÷ 830 = -0.23012048192771084
-0.23012048192771084 x 100 = -23.01%