I've been working on a formula for this. Here is what I have so far.
N_t = Number of razors at time t
t = time since joining SRP
I = Disposable Income
M = Years of Marriage
V = How much you value your marriage
S = Sneak index - how well you can hide purchases from your spouse. Related to M and V in a non-trivial way.
The formula goes something like this ( it is still a work in progress):
N_t = ceiling[ (S/M*V^2) * exp{k*I*t/V}]
k is a constant, yet to be determined. I call it Jimbo's Constant, and I am pretty sure the man (or woman) who finally discovers its value will win a Nobel Prize.
Ceiling[x] just means the smallest integer (whole number) not less than x.
James.