The following formulas are used:
((x(t)/x(t-1)) - 1) * 100
Percent Change from Year Ago
((x(t)/x(t-n_obs_per_yr)) - 1) * 100
Change from Year Ago (where the indicator is already in percent. ie: Unemployment Rate)
x(t) - x(t-n_obs_per_yr)
'x(t)' is the value of series x at time period t.
'n_obs_per_yr' is the number of observations per year. The number of observations per year differs by frequency: