Two examples of SPC I know of both had 'time' as a measurable characteristic with one sided spec limit (only upper) :
1. Time taken at the counter for checking out frim a five star hotel
2. At an Electronic Goods service station, time required to attend to customer's complaints.
Variable charts were used to monitor the process, and it was improved by identifying and removing assignable causes in the system.
A friend of mine has done research in this subject. I'll discuss with him and post any interesting points here.
-Atul.
