 The first step in sampling is calibration of the sampling pump. You must know the sampling rate and sampling time to determine the volume of air that passed through the filter. Remember, for our system, the sampling rate is 1.7 liters per minute. Dust concentrations are written in terms of weight per volume of air, or milligrams of dust per cubic meter of air. The sampling rate multiplied by the sampling time equals the volume of air sampled. We are using an electronic calibrator. These are very popular and accurate devices. Connect the filter to the pump so that air is drawn through the calibration device as well as the sampling train, complete with the filter. The sampling train for calibration must include the filter because it produces resistance to air movement and to the pump. The calibration would not be accurate without the filter in place. The sampling train is all the components that must be attached to each other to accurately collect the restvable dust sample. If your calibrator is different than the one shown, just follow the instructions provided. Turn on the fully charged pump and the calibrator and generate a bubble by pressing the bubble initiator button. You do this a few times to wet the inside of the flow tube. Clear the calibrator and take five readings again by depressing the initiator button and reading the flow rate on the LCD display. The infrared device of the calibrator notes the time for a bubble to travel a given distance and a flow rate is shown on the display screen. If the flow is below or above 1.7 liters per minute, adjust the pump flow rate, higher or lower, using the flow adjustment set screw. MSHA procedure is flow rate must be within 5% of target flow rate. Pumps should be calibrated before and checked after each sampling event. A sampling event could be a day of sampling or any continuous sampling period. These readings should be recorded on your calibration sheet. Before and after readings should be essentially the same. MSHA procedures require the post-calibration check to be within 5% of the pre-calibration. Compare your pre and post-sample calibration. Are both within 5% of 1.7 liters per minute? Are both within 5% of each other? The reasons a pump does not maintain flow are many. For example, if before was 1.7 liters per minute and after was 1 liter per minute, you might question the validity of your sample. What caused the drop? Excessive dust that overwhelmed the pump or low pump battery? You should also calibrate the pump as near the sampling site elevation as practical. Consult the calibrator instructions if calibration is not performed within 1,000 feet elevation of the sampling site. You may have to do some calculations to adjust for the elevation change.