In any BoM line, fill the `Quantity Formula` field.

The following values are available:

- `bom_line`: the current BoM line,
- `production`: the production order being created,
- `product`: the Product of current BoM line,
- `product_uom_qty`: the quantity of the production order line,
- `product_uom`: the UoM of the Product of current BoM line,
- `operation`: the operation where the components are consumed for current BoM line,

The computed quantity must be assigned to the `quantity` variable.
