PINPOINT High-Precision pH Calibration Fluids: 4.000 +/- 0.002, 7.000 +/- 0.002, 10.000 +/- 0.005. These come in plastic envelope packets and are extremely accurate and field portable. Each packet contains ample fluid for calibration (about 30 ml). There is a free sample of these included with each PINPOINT pH Monitor and PINPOINT pH Controller. All electronic pH instruments should be calibrated monthly.