For defining alternate Unit of measure, we have Item Unit of measure. However, in some cases some UOM conversion ratio may not be fixed. For e.g. conversion from Kilogram to Liters, this may differ time to time for the same item. In such case, the inventory quantity in base UOM may be different for lot to lot. So, it seems it will be helpful for defining a UOM conversion ratio specific to lot batches along with Item Unit of Measure.