New column : "coefficient"

Hi !

Is it possible to create a new optional column "coefficient"

I'm in a renting business and when the duration is more than 1day, we put a coefficient like this :

- 1d = 1

- 2d = 1,5

- 3d = 2

...

For moment I will to multiply every product...

So if there was a coefficient column it was wonderfull for renting business guys !

Thanks