Planning the harvest...But i need a magnifier

Im needing to buy some type of magnified tool so i can determine when to harvest, im at around 6 week flowering. What type, what power and where did you buy yours? Thanks

http://www.ebay.com/itm/Mini-Jeweler-Loupe-LED-Light-45X-Magnifier-Microscope-/270866149728?pt=LH_DefaultDomain_0&hash=item3f10e17160

This works better than it has any right to. It's easy to view the trichs right on the plant; no need to remove a leaf. FWIW, it's what I use.

Simon