Estimating the Cost of High-Quality Documentation
http://www.ingentaconnect.com/content/stc/tc/1995/00000042/00000001/art00009
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  peer-reviewed

Cover, Martha, David Cooke and Matt Hunt
Technical Communication Online
1995

Abstract:

The cost of developing a typical end user document at Cadence Design Systems is about $40,000. The cost of not providing complete and completely accurate documentation can be in the hundreds of thousands of dollars.