The performance of conductivity probes are affected by use due to residue build up and aging. Milwaukee TDS Calibration Solution 1382 ppm (M10032B) is a lab grade 1382 ppm TDS solution standard prepared against a NIST traceable potassium chloride solution that allows you to recalibrate your conductivity meter or tester. Check your meter or tester's manual to find the correct calibration standard for your meter. TDS readings are effected by temperature. To help with this, a chart of the actual ppm value at various temperatures is printed on each sachet. Milwaukee TDS solutions are labeled with the lot number and expiration date and packaged in an air tight, tamper-proof sachet.b>Milwaukee TDS Calibration Solution 1382 ppm+ fundamental for accurate TDS measurement+ factory calibrated with potassium chloride NIST 2202 SRM (Standard Reference Material) in deionized water for analytical use in accordance with ISO 3696/BS3978+ sealed against light and air+ ideal for on-the-spot calibration+