Official/Internal Lots 
IS-U devices are grouped into lots for purposes of inspection or certification.
Lots can be either official or internal.
You can use an official lot in order to certify several devices via the sampling procedure.
You can use an internal lot in order to carry out company inspections on devices that by law are not subject to certification or inspection.
Lots may contain the following:
Code defining the lot as an official or an internal lot
Lot status
Compilation date
Date on which lot devices were determined
Lot size
Drawing date
Next due year
Break-up date
The lot number is entered in the device master record of the lot device. This entry is used to determine the next replacement year of the device, depending on the status of the lot.