Given 2 exchange rates in terms of a Base Currency and a Quote Currency we can calculate appreciation and depreciation between them using the percentage change calculation. Letting e1 be the starting rate and e2 the final rate.
The percentage change of the Quote Currency relative to the Base Currency is ((e1 - e2)/e2) * 100.
The percentage change of the Base Currency relative to the Quote Currency is ((e2 - e1)/e1) * 100.
A positive change is appreciation and a negative change is depreciation.
For example, calculating between GBP and INR; if a year ago 1 GBP = 42.553 INR and today 1 GBP = 54.054 INR we have e1 = 42.553 and e2 = 54.054.
The percentage change of INR relative to GBP is ((e1 - e2)/e2) * 100 = ((42.553 - 54.054)/54.054) * 100 = -21.277%; Relative to GBP, INR Depreciated 21.277%.
The percentage change of GBP relative to INR is ((e2 - e1)/e1) * 100 = ((54.054 - 42.553)/42.553) * 100 = 27.027%; Relative to INR, GBP Appreciated 27.027%.