If you have a steady consumption rate, it is easy to forecast how far you can go with that rate – for example, if you know your car on average drives 20 kilometers per liter fuel and it has 30 liters left in the tank, you can simply multiply to know that you can drive 600 kilometers before you run out of fuel.
But if the consumption is not steady, you need something else. If the Good Beer Trading Co sells a particular seasonal Christmas beer, it is not simply a steady 100 beers sold per month – June will sell very few of those beers, while December sells hundreds. ...
