HI 991003 is the first pH meter that can measure pH, pH-mV (to check the electrode status), ORP and temperature with only one probe. Since ORP measurements are strongly effected by pH levels, HANNA® has developed the first meter that simultaneously measures both ranges. With all other instruments you need to switch the pH electrode with an ORP electrode (or vise-versa) and, therefore, it is impossible to have both measurements at the same time. HI 991003 is largely used to control plating bath waste water, swimming pool water quality and potable water sanitizing processes. HI 991003 is provided with our unique Sensor Check feature that allows the user to establish the status of the pH electrode before performing measurements. The Sensor Check feature consists of a pH-mV scale that shows the characteristics (slope and offset) of the sensor, allowing the user to determine if the electrode is in good condition. HI 991003 is protected in a waterproof casing for use in humid and wet environments. It also features a large dual-level LCD that displays pH or ORP and temperature readings simultaneously. http://www.hannainstruments.nl/upload/files/manuals/manHI_991003.pdf