The CellOx® 325 is a dissolved oxygen sensor with integrated temperature compensation and membrane leak monitoring, which can be used in the lab as well as in the field. Its features include a quick response time (t99<60 s) and low-maintenance operation. Its fields of use include surface waters, measurements in wastewater treatment plants, BOD directions, but also industrial and other applications. It is filled with electrolyte and achieves a long dwelling time up to 6 months. The calibration vessel is part of the delivery.