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a <br /> meter to sound. This point is usually clearly visible on the probe. If it is not visible it should <br /> located by dipping the probe into a water container whore the contact can be clearly scan, then <br /> marked. The total length of the water level meter should correspond with the length of the <br /> measuring tape. In addition, the individual masks on the cable should correspond with the <br /> correct footage. If the cable does not match them ' <br /> g g tape then the difference Of consistent) <br /> should be calculated as a percentage, (Le, 100 foot cable measures 102 feet . 984®). All <br /> measurements with the-cable should-then be multiplied by 0.98 to correct for the error. If the <br /> individual footage marks are not placed correctly and are not consistent in their deviation, the <br /> instrument should be replaced. <br /> If the water level indicator is constructed of a cable then c�libration will be peifornmed once per <br /> year. If there is a discrepancy, the conversion factor will be marked directly on the instrument <br /> Water level indicators constructed of tape are more subject to stretching and should becalibrated <br /> every 6 months and marked with the appropriate conversion.. <br /> Calibration data for each instrument will.be.recorded_and keptin a.binder:at the:office for-future..• - <br /> reference. The most recent calibration results will also be recorded in the technicians field notes_ <br /> There is no specific form for water level indicator calibration. <br /> pH Meter <br /> pH is subject to significant variations due to temperature, buffering capacity of the water, and <br /> instrument drift For this reason pH meters must be*calibrated before and after sampling on each.. <br /> day and at least once more during the day. To calibrate a pH meter the instrument reading is <br /> adjusted to read correctly for solutions with a standard pH_ _ <br /> Standard solutions are mixed fresh, according to package instructions,.for each sampling-event. <br /> Standard solutions or powders for pH 4, 7, and 10 are commercially available. These standards <br /> .are purchased fresh and discarded after shelf life has expired. Shelf lives vary depending on the <br /> brand of standards used. If pre-prepared solution is used,the expiration date of the solution will <br /> be noted on the calibration log.. <br /> Although different brands of pH meters vary, calibration pmcvh= are similar for all of them. <br /> A genailized generalizedcalibration procedure follows: <br /> I. Tum on the instrument, check the battery, and allow to warm up if necessary.. <br /> 23-493 944-FO 1%23 1 OR325 A-Z .taty 14,x000 <br />