HM Digital 1000ppm TDS Calibration Solution NaCl calibration solution, available in 342 ppm or 1000 ppm Comes in lightweight HDPE plastic bottles Sealed with a coated foam liner Laboratory quality NIST-traceable solutions Any brand TDS meter can be calibrated to any brand of calibration solution Bottles have a convenient wide mouth, allowing a user to simply insert the meter into a stable bottle Sealed with coated foam liner