There are rules

Many experts, through much research, have compiled golden rules of

documentation writing. These rules apply regardless of medium:

• Use short, simple, familiar words

• Avoid jargon.

• Use culture-and-gender-neutral language.

• Use correct grammar, punctuation, and spelling.

• Use simple sentences, active voice, and present tense.

• Begin instructions in the imperative mode by starting sentences with

an action verb.

• Use simple graphic elements such as bulleted lists and numbered

steps to make information visually accessible.

From: The Principles of Readability

get it here, http://www.impact-information.com/impactinfo/readability02.pdf

Flesch–Kincaid readability tests

from Wikipedia,


yeah,


I KNOW!

http://en.wikipedia.org/wiki/Flesch-Kincaid_readability_test

The Flesch/Flesch–Kincaid readability tests are readability tests designed to indicate comprehension difficulty when reading a passage of contemporary academic English. There are two tests, the Flesch Reading Ease, and the Flesch–Kincaid Grade Level. Although they use the same core measures (word length and sentence length), they have different weighting factors. The results of the two tests correlate approximately inversely: a text with a comparatively high score on the Reading Ease test should have a lower score on the Grade Level test. Rudolf Flesch devised both systems while J. Peter Kincaid developed the latter for the United States Navy. Such readability tests suggest that many Wikipedia articles may be "too sophisticated" for their readers.^[1]

more at link...

there's a software....
http://www.gnu.org/software/diction/