We must keep track of the impact of these assumptions. Frequently, these simple models can be very informative. While we would not use them on a daily basis to track production, they can be extremely useful in weighing alternatives or evaluating potential changes. Processing time through each station includes prior processing time on all product, including yield loss. Again, remember that manufacturing lead time is based on processing of batches.
Cost is on a per-lens basis.
Production time ratio is very good, but efficiency is lower than we might like due to yield losses. Station 5 also has the highest yield loss. There is significant loss of efficiency due to yield. Improvement in this area should address causes of failures in station 5. Thus we would look at all prior stations.