hair is read like a time line and grows from the scalp---the ends will show usage and that's what they clip for the test---most peeps will get a haircut before testing because they want the newest growth tested---not the older ends---if i remember correctly 90 days average growth is 1 1/2"---best of luck
For hair to give some its roots in the lab to determine the disease whether it is dandruff or alopacia which is very typical disease,so this thing gives more better facility to do the treatment of the patients.