-2.97% is the change from 639 to 620
Calculation steps:
[( 620 - 639 ) ÷ 639] x 100 = -2.97%
Formula
Percentage change = [(620 - 639) / 639] x 100
Subtract the new number by the original number
620 - 639 = -19
-19 ÷ 639 = -0.0297339593114241
-0.0297339593114241 x 100 = -2.97%