Understanding Gold Content: How % Relates to Karat Stamps on Jewelry

Question
I have a question concerning how different % of gold content relates to karats that are stamped on jewelry.  
  This gold ring that I have is stamped 10k.  However, I took it to an expert who told me that the gold content is 38.5%.  
  I am aware that 9K = 37.5% and that 10k = 41.7%.
  However, considering that my gold ring is closer to 9k, should it have been stamped 9k, instead of 10k?  In other words, what is the minimal % amount of gold that must be in 10k for a jewelry piece to be labeled 10k?

Answer
Hi Laura, you are actually correct. I'm not sure why it was stamped 10k instead of 9k if the expert's analysis of your gold is accurate, but a millesimal fineness of 41.7% (417 on the scale of 333 to 999.999) is required for gold to be considered 10k.

Regards,
Jonathon
http://www.brilliance.com