The HI96738 portable photometer is for the measurement of chlorine dioxide. Hanna's portable photometers feature an advanced optical system; the combination of a special tungsten lamp, a narrow band interference filter, and silicon photodetector ensure accurate photometric readings every time. The Hanna exclusive CAL Check™ feature utilizes ready-made, NIST traceable standards to verify both meter validation and calibration. The exclusive cuvette locking system ensures that the cuvette is inserted into the measurement cell in the same position every time to maintain a consistent path length. Features at-a-glanceCAL Check™ - Allows for performance verification and calibration of the meter using a CAL Check NIST traceable secondary standard.GLP - Records the date of the last user calibration performed.Built in timer - Ensures the appropriate reaction time is used for the chemical reaction. At the end of the timer the meter will automatically take the reading. This feature ensures consistency across multiple users.Indexing indent on meter - The meter has an indent that allows for a lock and key fit with the cuvette cap. This ensures that the cuvette is indexed consistently (same position) in order to maintain the same path length for accurate results.Cooling Lamp Indicator - It is necessary to maintain a consistent temperature of the optical components in order to maintain a narrow wavelength band of light. This photometer has a cooling lamp indicator that is displayed for a short period of time before each measurement in order to allow the components to cool and obtain the highest accuracy possible.Error messages - Messages on display alerting to problems including no cap, over range and under range readings, and light source error.Auto-shut off - Automatic shut off after 10 minutes of non-use when the meter is in measurement mode. Prevents wastage of batteries in the event the meter is accidentally not turned off.Battery status indicatorThe instrument has a battery level indicator to display reaming life as follows:• 3 lines for 100 % capacity• 2 lines for 66 % capacity• 1 line for 33 % capacity• Battery icon blinks when the capacity is less than 10 %.Units of measure - Appropriate unit of measure is displayed along with reading.