The new dual TDS panel-mounted controller from HM Digital Inc., of Los Angeles, is effective when monitoring the performance of commercial RO systems. The unit is equipped with two sensors that test for TDS in the feed water as well as the product water. The bright LED display alternates between the two readings with the push of a button. It monitors water up to 999 ppm. When the reading in the out mode rises above the preset point, the alarm sounds and the relay control will shut off the pump.