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N 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, then- . marked. The total length of the water level meter should correspond with the length of the measuring tape. In addition, the individual on the cable should correspond with the correct footage. If the cable does not match the measuring g tape then the difference(nf consistent) should be calculated. as a percentage, (Le.; 100 foot cable measures 102. feet = 981®). All 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 am not consistent in their deviation, the instrument should be replaced. If the water level indicator is constructed of a cable then c 'oration 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 becalilibrated every 6 months and marked with the appropriate conversion.. Calibration data for each instrument will.be-record -and keptin a.binder at the;office forfuture_ : - reference. The most recent calt'bration results will also be recorded in the technicians field notes. There is no specific form for water level indicator calibration. PH meter pH is subject to significant variations due to temperatym, buffering capacity of the water, and bstrument drift-for this reason pH meters most be-calibrated.before and after sampling on each.. day and at least once more during the day. To calibrate a pH meter the instrrurnent reading is adjusted to read correctly for solutions with a standard pH. Standard solutions are mixed f vrA according to e ' 'ons,-for each sampling event. Standard solutions or Powders for pH 4,7, and 10 am COMInCrciallY available. These standards -am..p=based fresh and-discarded after shelf life 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 caRbration log. Although different brands of pH meters vary, cast 'on pMCxfi= are similar for allof thern.- A generalized calibration procedure follows: 1. T'uxn on the Instrument,check the battery.and ow to warm up if necessary:. _- 23-493949.Fo 1123 1OR32$ A-2 My la,2000 zoov xkwewa.nom.