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p meter to sound. This point is usually clearly visible on the probe. If it is not visible it should located by dipping the probe into a water container where the contact'can be clearly seen, Lhen l. marked. The total length of the water level meter should correspond with the length of the measuring tape_ In addition, the individual marks oa the cable should con=pond with the comet footage. If the cable does not match the measuring tape then the differenceCif consistent) should be calculated. as a percentage, (Lel., 100 foot cable measures 102 feet 98°!0). All measurements with the'cable should-then be .multiplied by 0.98 to correct for the error. If the individual footage marcs are not placed correctly and arc not consistent in their deviation, the instrument should be replaced. If the water level indicator is constructed of a cable then calibration will be performed once per year. If there is a discrepancy, the conversion factor will be marked directly on the instrument. Water level indicators constructed of tape are more subject to stretching and should be calibrated every 6 months and marked with the appropriate conversion.. Calibradon data for each instrument will.be.recorded.and.kepUa a.binder at the:office forfuwre_ - reference. The most recent calibration results will also be recorded in the technicians field notes. There is no specific form for water level indicator calibration. 2H Meter pH is subject to significant variations due to temperature, buffering capacity of the water, and instrinnent drift For this reason pH meters must be-calibrated.before and after sampling on each.. day and at least once more during the day. To calibrate a pH meter,the instrument 'reading is - adjusted to read corrccdy for solutions with a standard pK Standard solutions arc mixed fresh, according to package instrcQ ,-for each satnpling'event. Standard solutions or powders for pH 4,7, and 10 are commercially available. These standards -are purchased fresh and-discarded after sheff life has expired. Shelf livesvary depending on the brand of standards used. If pre-prepared solution is used,the expiration daze of the solution will be noted on the calibration log. Although different brands of pH meters vary, raltbration procedturs are similar for an of them. A geaerali calibration procedure follows: 1. Turn on the instrument,check the battery,and allow to wartit up if necessary.. -- 23.493$49•FOIt23IOR325 A•Z J*14,2404 COPYrf t ZWO KkW Wa.baa.