What is the formula for calculating constant percent change?

For the period from ##t_1## to ##t_2## for some state ##f(t)## with a constant percentage change, that constant percentage change is given by: ##color(white)("XX")(f(t_2)/f(t_1)-1)*100%##

The actual change from ##t_1## to ##t_2## is ##color(white)("XX")f(t_2)-f(t_1)##

The change as a fraction of its value at ##t_1## is ##(f(t_2)-f(t_1))/f(t_1) color(white)("XX")=color(white)("XX") f(t_2)/f(t_1) -1##

or, as a percentage: ##color(white)("XX")(f(t_2)/f(t_1)-1)*100%##