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The standard deviation (estimate of random error) is the quantitative measure of precision (Table 4). The targets for precision are applied to the standard deviation of O-B over a certain period for each of the observed variables (Table 6). Like trueness, precision will be assessed 6-hourly, daily and monthly. Also, the 5-day moving average (Alert) of daily calculated standard deviation of O-B (Table 9) will be calculated for all variables and compared to the respective prescribed threshold ( Table 6). This together with the performance indicator for Trueness will be used by the Evaluation function on their daily monitoring activities to determine the level of priority for stations showing accuracy/measurement uncertainty issues (see table in Annex2 of WDQMS Guidance Document).
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