Digital Conductivity/TDS Meter Model 641 is an accurate test instruments for measurement of Conductivity and TDS of aqueous solutions. It uses the latest microcontroller technology to measure the Conductivity from 200 µS to 1000 mS and TDS from 200 ppm to 1000 ppt in 5 ranges respectively. The appropriate range is automatically selected by the instrument. The Resolution is 0.1 µS for Conductivity and 0.1 ppm for TDS in the lowest range. The cell constant is flashed on a digital display and can be adjusted from the front panel. Facility is also provided for automatic measurement of cell constant with a known standard solution.