text: An alternative method of providing redundancy in the control system is to recalibrate the sensors periodically during the dive by exposing them to a flow of either diluent or oxygen or both at different times, and using the output to check whether the cell is reacting appropriately to the known gas as the known depth. This method has the added advantage of allowing calibration at higher oxygen partial pressure than 1 bar. This procedure may be done automatically, where the system has been designed to do it, or the diver can manually perform a diluent flush at any depth at which the diluent is breathable to compare the cell PO2 readings against a known FO2 and absolute pressure to verify the displayed values. This test does not only validate the cell. If the sensor does not display the expected value, it is possible that the oxygen sensor, the pressure sensor (depth), or the gas mixture FO2, or any combination of these may be faulty. As all three of these possible faults could be life-threatening, the test is quite powerful.
  Testing
  The first commercially available certified oxygen cell checking device was launched in 2005 by Narked at 90, but did not achieve commercial success. A much revised model was released in 2007 and won the "Gordon Smith Award" for Innovation at the Diving Equipment Manufacturers Exhibition in Florida. Narked at 90 Ltd also won the Innovation Award for "an technical diving product that has made diving safer" at EUROTEK.2010 for their Oxygen Cell Checker. . The Cell Checker has been used by organisations such as Teledyne, Vandagraph, National Oceanic and Atmospheric Administration, NURC (NATO Undersea Research Centre), and Diving Diseases Research Centre.
  A small pressure vessel for hyperbaric testing of cells is also available in which a pressurised oxygen atmosphere of up to 2 bar can be used to check linearity at higher pressures using the electronics of the rebreather.