A key aspect to applying an x and r-chart model to a variable quality measure is the concept of chance and assignable causes. Consider the following context for the two questions below. Suppose that during your commute to school in the morning you often stop at MacDonald's for a caramel latte made with 2% milk. You always park your car, walk into the restaurant, order your latte at the counter with three shots of caramel sweetener (instead of the usual five) and with 2% milk, pay with a credit card get two napkins while waiting for your latte, receive your drink, and walk back to your car. Assume the process begins when you leave your car and ends when you return to your car. The quality measure is the time to complete the entire process.
1. What would be the three chance (common) causes of variation for this process?
2. What would be for assignable (special) causes of variation for this process?