The function MT returns the value of (1+i)n where i and n can be any floating point numbers. Instead of reporting an overflow error for values which cannot be computed (eg. i=-1, n=-1) MT returns 1. If the returned value would be too large, a modulated value is returned. It is therefore imperative that the programmer takes care that the parameters are correct, otherwise the return values may not make much sense.
MT gives you a factor which indicates the increase (i>1) or decrease (i<1) of capital at an interest rate i over a number of periods n. The gain is known as compound interest. If you give any sum to a bank at an interest rate of five percent (ie. annual 5 per 100 increase) for (say) ten years, you will gain 62.9% because: MT(0.05, 10) = 1.628895
approximates EXP(1) for large values of n.