Also....
I prefer to use the older ratio of 9.58 Years of the Sun to 1 Year of the Trees because the later ratio of 144 Years of the Sun to 1 Year of the Trees is very inconsistent with many texts. The fact that it coincides with the Yen described in the appendices to The Lord of the Rings probably means only that Tolkien wasn't considering the other texts, then unpublished, because he was in the process of revising the entire (unpublished) mythology.
-from an article by Michael Martinez entitled "Elves by the numbers"
http://www.suite101.com/article.cfm/tolkien/54681
I won't go to the trouble of quoting the texts refering to the 144 and 9.58 years. It's all very unresolved.