Variance in Order Price Quantity 
The unit in which a material is priced in a purchase order is called the order price unit.
Example
100 pieces of a material are ordered, each at $20 a kg. In this case, "pc" (piece) is the order unit, and "kg" (kilogram) is the order price unit (OPUn). With this type of purchase order, the conversion factor for piece and kilogram must also be specified so that the system can convert quantities of one unit of measure into the other. For example:
4 pieces equal 10 kg.
A variance in order price quantity applies in the following cases:
Invoice receipt after goods receipt
The ratio
invoiced quantity in OPUn : invoiced quantity in order units
deviates from the ratio
quantity of goods received in OPUn : quantity of goods received in order units.
Invoice receipt before goods receipt
The ratio
invoiced quantity in OPUn : invoiced quantity in order units
deviates from the ratio
quantity ordered in OPUn : quantity ordered in order units