Hi, very new pool owner. I tested my CYA with the K-2006. The tests were consistent with a CYA between 60 & 70. When I read pool school it said the results are +- 15PPM so I am wondering what would i base my CYA readings on? The 60 or the 70 or is it 60-15=45 or is it 70+15=85?Confused???