Control Wizard Products 442-1500 PPM Buffer Solution 4 oz. bottle.

Used to calibrate Myron L. & other TDS meters that use the 442 standard or .7 ratio of PPM to EC standard.Suitable for meters that use the horticultural/agricultural standards of .68 and .7. This is to say that 1 EC is = to 700 ppm total dissolved salts (TDS). Older style meters would use the water standard or .5 calibration solutions of 1382 ppm.