# Time Constant Tool: y = exp(x/400)

We'll start with this simple equation: y = exp(x/400); an increasing exponential curve.

We can see the general shape of exponential growth and decay curves:

We can take the decay curve (that is, the one with the minus sign: *e*^{-x}) and amend the mathematical formula in order to create equations which accurately describe the decay of transverse magnetisation (M_{xy}), and the recovery of longitudinal magnetisation (M_{z}).

Navigate below to the next equation in the list: exp (-x/400).

Remember, T1, T2 and T2* are time constants.