The HI96715 portable photometer is for the measurement of ammonia (as NH3-N) in freshwater samples. Hanna's portable photometers feature an advanced optical system; the combination of a light emitting diode (LED), a narrow band interference filter, and silicon photodetector ensure accurate photometric readings every time. The Hanna exclusive CAL Check™ feature utilizes ready-made standards traceable to a NIST Standard for performance verification 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.