-6.85% is the change from 686 to 639
Calculation steps:
[( 639 - 686 ) ÷ 686] x 100 = -6.85%
Formula
Percentage change = [(639 - 686) / 686] x 100
Subtract the new number by the original number
639 - 686 = -47
-47 ÷ 686 = -0.06851311953352769
-0.06851311953352769 x 100 = -6.85%