Chapter 4
Achieving Single- Piece Flow
Around 2:00 p.m. on Thanksgiving Day,
as guests began to arrive, Belinda Daniel
took the turkey, glistening and brown,
out of the oven. She had left just enough
time to whip up some gravy on the
stovetop and warm up the mashed pota-
toes and sweet potato casserole that had
been cooked the day before.
As her friends and family entertained
themselves and waited for mealtime,
Belinda peered into cabinets that had
not been cleaned out in over a year and
failed to find any flour for the gravy. All
the activity was starting to give her a
headache, so she took some ibuprofen.
“I need to go to the store,” she announced to no one in particular. “I’ll
be right back.
Belinda Daniel takes a break from her
Thanksgiving preparations and her
houseguests to pop out to the grocery
store for a few last- minute items. While
checking out at the self- checkout line,
she thinks about different designs for
checkout lines and their effect on cus-
tomer wait times. She considers how to
determine the quantity that should be
processed at the same time.
As you read Belinda’s story, think
about the different reasons that might
exist for identifying an optimal batch
size, and the relationship between
batch size and wait time. What do
stores consider when designing check-
out lines?
At the grocery store, many other people were taking short breaks from
their cooking duties to pick up last- minute items. Belinda grabbed a
basket, found the flour and some detergent, and pondered whether to
use one of the traditional grocery store lines or a self- serve express
lane. She wasn’t in a hurry to return to her kitchen, but the store was
warm and noisy, and she wanted to get back outside to the cooler air to
help her headache.
The lines were longer at the self- serve stations, but each customer had
only one or two items. Although the full- service lines were shorter,
the customers in them had carts that were full to overflowing. Belinda
went with a line for one of the six self- checkouts.
While Belinda waited, she watched a few of the full- service lines to see
if people in those lines got through before she did. One line lacked a
bagger, so checked cans and cartons slid up against bread and lettuce.
At another line, an elderly man squinted at the total above the cash
register and then began writing in his checkbook, at the same time
chatting with the clerk. She could see the light flashing at another cash
register, indicating the need for a price check. Meanwhile, six people
ahead of her in her self- checkout line had finished with the process.
As Belinda had watched her line and the other self- checkout lines, she
had seen delays from time to time as customers had trouble entering
their frequent- shopper numbers or finding the barcodes on items. A
store employee helped customers get through the self- checkout sta-
tions. Belinda felt that she had chosen the right service line.
She had also been watching the store’s bagging system. At other stores,
self- serve checkout stations used a half- length conveyor belt system;
customers scanned their items and then placed them on the belt.
Scanned items moved along the belt, where they stayed until the cus-
tomer paid for them and then placed them in bags.

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