Is there any way to match a speedometer cluster to a particular vehicle (911) via the serial number on the cluster? 
Let me add that a friend of mine wants to purchase a vehicle and ask me to check the miles against the the working hours on the DME. with my tester. I found that the working hours were a little high but not completely out of an acceptable range. I could be wrong however i use this method 20 K miles usually turns up around 550 hours on the DME. Does this calculation sound close?