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K . z meter to sound. This point is usually cleaily visible on the probe. If it is not visible it should s i located by dipping the probe into a water container where the contact can be clearly seen, then- ). marked. The total -length of the water level meter should correspond with the length of the measuring tape. In addition, the individual marks on the cable should correspond with the correct footage. If the cable,does not match the measuring tape then the difference (if consistent) should be calculated as a percentage, (i.e., 100 foot (:able measures 102 feet == 9$®/®), A Il measurements with the-cable should-then be multiplied by 0.98 to correct for the error. If the individual footage marks are not placed correctly and are not consistent in their deviation, the instrument should be replaced. If the water level indicator is constructed of a cable then c A'bration 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.. Calibration data for each instrument will.be.recorded.and keptin a binder.at the:office forfuture_•: reference. The,most recent calibration results will also be recorded in the tecbnicL ns field notes.. there is no specific form for water level indicator calibration. VH Meter pH is.subject to significant variations due to temperature, buffering capacity of the water, and - instrument 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 correctly for solutions with a standard pFL Standard solutions.are mixed fiesh, according to package instructions,for each sampling event 'Standard solutions or powders for pH 4, 7, and 10 are Commercially available- These standards Zee P and'discarded after shelf life has Shelf lives vary depending on the brand of standards used, if°pre-Prepared solution is used,the expiration date of the solution will be noted on the calibration log. Although different brands of pH meters vary, calibration on ures are similar for all of them. A generalized calibration procedure follows: 1. Turn on the instrument,check the battery,and allow to warm up if nee 23493 949-FO M I OR325 A-2 July 14,2000 z000 ktctntCMa.tae.