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Using Specifications

Combining the allowable accuracies of the calibrator/control and the osmometer provide the expected range of the mean for a series of tests.  The osmometer repeatability specification is not considered when determining this combined accuracy.

For example, assume that the specifications are:
     Formulation tolerance of 290 mOsm/kg H2O (nominal) control solution:
                                                               ±2 mOsm/kg H2O
     Osmometer linearity specification:    ±1%

     Converting the linearity percentage to a mOsm/kg H2O value at the
     nominal value of 290 mOsm/kg H2O gives:
                                                              ±2.9 mOsm/kg H2O

     Thus the combined accuracy of the control solution and the
      osmometer is
           ±2 mOsm/kg H2O + ±2.9 mOsm/kg H2O =  ±4.9 mOsm/kg H2O

     Therefore the acceptable range of values for the mean of a set
     of results is:
          290 mOsm/kg H2O ±4.9 mOsm/kg H2O, or     285.1 to 294.9 mOsm/kg H2O.

Now consider the osmometer repeatability.  If the osmometer repeatability
specification is stated in terms of a standard deviation and has a
value of:
                                                    1s or 1 S.D. =  2 mOsm/kg H2O

and the actual standard deviation calculated from a set of data is ≤ 2 mOsm/kg H2O, then the osmometer is performing acceptably from a repeatability standpoint.

Using the acceptable range of values for the mean from above and a 1 standard deviation value for the repeatability, the acceptable range of results for any individual sample tested within the data set is:
           Lower range limit:    285.1 - 2 = 283.1 mOsm/kg H2O
           Upper range limit:    294.9 + 2 = 296.9 mOsm/kg H2O.

Using a repeatability value equal to 2 standard deviations, the acceptable range of results for any individual sample tested within the data set is:
           Lower range limit:    285.1 - (2 X 2) = 281.1 mOsm/kg H2O
           Upper range limit:    294.9 + (2 X 2) = 298.9 mOsm/kg H2O.

Therefore, with this osmometer and testing this calibrator/control, if the mean of a series of test results lies between 285.1 and 294.9 mOsm/kg H2O and the standard deviation of that group of test results is ≤ 2 mOsm/kg H2O, then the complete system (i.e. calibrator/control and the osmometer) is performing acceptably with an acceptable range of results as determined above.