Hannas most advanced series of pH meters actually monitor the parameters that most frequently contribute to inaccurate pH measurements. It will prompt the user to clean the electrode and will indicate "contaminted buffer" when appropriate.It even monitors the electrode response time. These meters have an advanced CalibrationCheck"¢ feature that lets the user know when its time to recalibrate, when the electrode requires cleaning or replacement and when an incorrect calibration solution has been used.