You probably should get a model.
If the "return" over 'n' is 'i', then perhaps:
Solving for i:
That's enough. You can see that exponents can lead to logarithms.
On the other hand, perhaps it is thought that NewPrice/OldPrice gets too big too fast and studying the logarithm is more tractable.
On still another hand, there may be some statistical significance and absent the logarithm the statistical measure shows some inappropriate bias. Suffering the logarithm transformation might straighten it out.
In other words, any number of reasons.