5. Use of Internal Laboratory Data

5.1 Modeling Approach

The modeling approach involves establishing a mathematical relationship—often based on a physical or chemical principle—between the measurand (output variable) and the various influencing variables (input variables).

It is divided into four steps:

• Step 1: Modeling the measurement process (measurement model);

• Step 2: Evaluation of characteristics (standard uncertainty, etc.) for each input variable;

• Step 3: Estimation of the output quantity (measurand);

• Step 4: Expressing the final result.

The historical intra-laboratory uncertainty evaluation procedure presented...