Readability is the Only Metric

What you can measure, you can improve.  Whether you need creative content for e-commerce or step-by-step instructions for machine repair, you must reach your audience.   Microsoft Word offers metrics for readability, from the Grammar and Spelling checker, under Tools.   We have no quantified methods for creativity, invention, cleverness, or insight.  We can measure word length, sentence length, and sentences per paragraph.  

It is not perfect. In fact, it can be gimmicked, tricked, and gamed.  But it works.  On a project to develop a multiprocessor industrial controller, the other technical writer was a young guy from an advertising agency.  He did not know manufacturing, but he was good writer.  We enjoyed finding some of the many failings in the MS-Word readability scales. We still used them.  They proved that we documented the interactive debugger to a 6th grade reading level.  When the line is down, no one is looking for a literary experience. You need answers.

Texas Department of Information Resources
IT Policy - Originally at 12.9 reading level

Same IT Policy - Rewritten to 12.0 reading level.

Of the 300,000 main entries in the Oxford English Dictionary, only 3,000 are Basic English; and most of us speak only 10,000 distinct words.  The average college-educated American recognizes about 100,000 words.  Whether "fardels" in that list is putative.  So, Hamlet's rhetorical question might pass the readability score, but not carry meaning.  Whether "putative" is in your speaking vocabulary may be arguable.

The fact remains that we have an objective measure for readability. 

Also on Necessary Facts
Visualizing Complex Data
Documentation is Specification
The Art of Typography
 The Genius of Design
How to Hire a Technical Writer