Process-batch:

A Process-batch must be Variable both along Its Own Route and In Time

The process-batch at distinct levels of manufacturing: route-wise and time-wise both, should be different. Usually, we follow fixed batch-size unless exceptional situation come out. OPT argues against it. In OPT, lot size is a dynamic decision, which must change as per time and situation. It must be decided upon issues such as inventory level, set-up time/cost, flexibility, material handling, and agility of the system, uncertainty on the shop-floor in addition to in market, etc. It the resource is non-bottleneck, we may afford to have smaller process-batch; but if the resource is bottleneck, we must go for larger process batch.