Norsk Ferries operates daily round-trip voyages between Seattle and Vancouver using a fleet of three Quality Control ferries, the Sea Quill, the Neptune, and the Orcas. The budgeted amount of fuel for each round trip is the (LO 2,6)

average fuel usage, which over the last 12 months has been 150 gallons. Norsk has set the upper control limit at 180 gallons and the lower control limit at 130 gallons. The operations manager received the following report for round-trip fuel usage by the three ferries for the period:

Number of Gallons per Round-Trip Trip Sea Quill Neptune Orcas 1 156 ike) 146 2 144 141 156 3 146 144 167 4 152 161 156 cS) 156 138 183 6 161 170 177 7 167 149 189 8 186 159 We 2g 173 152 176 10 Ws 140 185 Required

a. Create quality control charts for round-trip fuel usage for each of the three ferries for the period.

What inferences can you draw from them?

b. Some managers propose that Norsk present its quality control charts in monetary terms rather than in physical amount (gallons) terms. What are the advantages and disadvantages of using monetary fuel costs rather than gallons in the quality control charts?