All Oakton conductivity/TDS calibration solutions are Cross checked using different Test methods, premixed, and ready to use. Oakton conductivity “Singles” pouches are convenient, air-tight pouches with high-precision calibration standards. Ideal for field use-take them to your Test site for on-the-spot calibration. Pouches are labeled with equivalent values for ppm in KCl, NaCl and 442 and conductivity values at 25° C and CAS numbers for “right-to-know” requirements. Each box contains twenty 20 ml pouches.