"Accuracy: 100% Full Scale �2% Dimensions: W 260 x H 60 x D 65mm For the calibration of low flow air sampling pumps and indicator tube hand pumps.Air flow is measured by the displacement of a near frictionless glass float in a glass cylinder. For calibration of flow pumps, flow rates are read directly from the scale after a measured time period (60 or 120 seconds) Measurements are unaffected by pulsating flows. With hand pumps, volume is measured from the same scale. Regular calibration of hand pumps is recommended as wear and corrosion of seals can cause under estimation of contaminant concentration. A certificate of calibration is supplied with each Dry Flo Calibrator"