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Heat the pH 4.01 and pH 7.01 solution to 25.0 Celsius.
Place the probe into the pH 4.01 solution. Leave it there for at least 5 minutes.
Start calibration procedure for pH 4 solution.
After 5 minutes, rinse in RO water, pat dry.
Place into pH 7.01 solution. Leave it there for at least 5 minutes.
Start calibration procedure for pH 7 solution.
Complete the calibration.
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