I think you will need another field which has dates in it, so, for
example, each day you record number of tools going out and then you
can add this in a cumulative sum column and subtract it from the
number of tools you have in your inventory.

It strikes me as a bit simplistic, though - if a customer wants to
hire a concrete mixer and you don't have any in stock (but you know
that you do have 300 other items), that's not really going to help -
shouldn't you also record the type of tools being hired out and then
keep track of each type?

Hope this helps.

Pete

On Feb 21, 7:09 pm, "oatmeal" wrote:
Just as an example, let's say I'm a rental company that rents tools
for long periods of time. I want to understand how many tools are
being rented, how many I have left in inventory still available to
rent, and when I am going to exhaust my inventory. So for instance, I
have the following three primary fields:

1. Number of tools out for rent.
2. Number of tools in inventory still available for rent.
3. Sales growth month over month.

So using the sales growth, I should be able to roughly predict when I
am going to run out of inventory (assuming my sales growth is going to
continue to rise.)

I can't wrap my head around the logic to be honest. The variable I
want is the number of days left until I am going to run out of tools
for run.

Any Ideas?