inventory unit sales unit

Hi,

We purchase cable roles, one cable role = 200meter

So, purchase unit = role 200m

In the warehouses we also transport complete roles and we want to see how many roles (NOT how many meters) we have in inventory, so inventory unit = role 200m (and not 'meter' because if we have 5 roles in inventory, we would see not 5 'roles 200m' but 1000 'meter' -> not user friendly!)

We sell to our customers per meter, so sales unit = meter.

But the problem is, when we sell for example 5meter or 120meter or ..., the inventory unit is also minus 1 but we still have almost a full role...for example: 5 roles in inventory, we sell 6 meter -> result is 4 roles in inventory...

Have someone a solution for this?

Thanks!

Frederik