Bluelab Ph 7.0 Calibration Solution 20ml Sachet Ph measuring equipment must be cleaned and calibrated regularly to ensure they are giving the user accurate readings Phinstruments arecalibrated to Ph7.0 first (buffer)then to Ph4.0 (slope) Bluelab's ec/cf equipment does not need calibrating as they are all factory calibrated The Cf27.7 (Ec2.77)Solution is used as a reference or checking solutionto ensure you have adequately cleaned the ec/cf probe