Dave€™s Burgers is a fast-food restaurant franchise in Nova Scotia, and Newfoundland and Labrador. Recently, Dave€™s Burgers has followed the lead of larger franchise restaurants like Burger King, McDonald€™s, and Harvey€™s and constructed drive-through windows at all its locations. However, instead of making Dave€™s Burgers more competitive, the drive-through windows have been a source of continual problems, and the company has lost market share to its larger competitors in almost all locations. To identify and correct the problems, top management has selected three of its restaurants (two in Nova Scotia and one in Newfoundland and Labrador) as test sites and has implemented a quality management program at each of them. A quality team made up of employees, managers, and quality specialists from company headquarters at the Halifax test restaurant use traditional quality tools like Pareto charts, check sheets, fish bone diagrams, and process flowcharts. The team determines that the primary problem is slow, erratic service at the drive-through window. Studies show that the time from a customer arriving at the window to the time the order is received averages 2.6 minutes. To be competitive, management believes service time should be reduced to at least 2.0 minutes and ideally 1.5 minutes.
The Halifax Dave€™s Burgers franchise implements a number of production process changes to improve service time at the drive-through window. It provides all employees with more training across all restaurant functions, improves the headset system, improves the equipment layout, develops clearer signs for customers, streamlines the menu, and initiates even-dollar (tax-inclusive) pricing to speed the payment process. Most importantly, the restaurant installs large, visible electronic timers that show how long a customer is at the window. This not only allows the quality team to measure service speed, but also provides employees with a constant reminder that a customer is waiting.
These quality improvements were implemented over several months, and their effect was immediate. Service speed obviously improved and market share at the Halifax restaurant increased by 5%. To maintain quality service, make sure the service time remains fast, and continue to improve service, the quality team decides to use an SPC chart on a continuing basis. They collect six service time observations daily over a 15-day period, as follows:

Construct a control chart to monitor the service at the drive-through window. Determine if your control chart can be implemented on a continuing basis or if additional observations need to be collected. Explain why the chart you developed can or cannot be used. Also discuss what other SPC charts Dave€™s Burgers might use in its overall quality-management program.

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Observations of Service Time (min) Sample 5 3 4 1.75 2.50 1.54 1.38 1.32 1 1.62 1.25 1.66 1.96 1.55 1.38 2.01 2. Observations of Service Time (min) Sample 1 3 4 1.85 1.01 0.95 1.79 1.66 1.94 4 3.10 1.18 1.25 1.45 1.09 2.11 5 1.95 0.76 1.34 2.12 1.45 1.03 0.88 2.50 1.07 1.50 1.33 1.62 1.55 1.41 1.95 1.14 1.86 1.02 2.78 1.56 1.87 2.03 0.79 1.14 1.31 1.05 0.94 1.53 1.71 1.15 10 1.67 1.85 2.03 1.12 1.50 1.36 11 0.95 1.73 1.12 1.67 2.05 1.42 12 3.21 4.16 1.67 1.75 2.87 3.76 13 1.65 1.78 2.63 1.05 1.21 2.09 14 2.36 3.55 1.92 1.45 3.64 2.30 15 1.07 0.96 1.13 2.05 0.91 1.66