Oakton 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. Each box contains twenty 20 ml pouches. All Oakton pH buffer solutions are freshness dated, and standardized against nist-traceable References to ensure quality. 0.01 pH at 25° C. Nist traceable materials labeled with pH vs. Temperature tables for accurate calibration