Uncle Bob's precious piece of wisdom

http://www.scrumalliance.org/articles/300-the-land-that-scrum-forgot
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How do you keep a Scrum Team from losing productivity?  

How do you make sure that hyper-productivity doesn’t veer headlong into a quagmire?  

You make sure that the team is not hyper-productively making a mess! 

You make sure they are practicing the disciplines that produce data that can be measured. 

You use that data to measure the quality of the code they are producing; and you provide incentives for keeping that code clean.