Environmental Factors Uncertainty Worksheet Features 
The Environment Parameter Table provides up to 10 environment parameter error sources for estimating the total measurement uncertainty due to environmental factors.  The data for each environmental error source can be input directly into the Environment Parameters table or the corresponding Tolerance Worksheet, which is activated by clicking the ID Number button to the left of the environment parameter name.

UncertaintyAnalyzer assumes that measurement uncertainties due to environmental factors are normally distributed unless the associated degrees of freedom are less than infinite or the % Confidence is 100%.  If  the degrees of freedom are less than infinite and the % Confidence is less than 100%, the Student's t distribution is used.  If the % Confidence is 100%, then the Uniform distribution is used and the degrees of freedom are assumed to be infinite.

Elements of the Environment Parameter Table are described below.

Parameter Name
The name or brief description of the particular environment parameter is entered in this column.  The type of environment parameter may be one of the following:

• An ancillary parameter or artifact that supports a measurement process but does not provide a direct reading of the quantity being measured. The ancillary parameter may influence the bias of the subject parameter or measuring parameter. An example of this type of environment parameter could be a power supply.

• A component of a measurement system that participates in the measurement process but does not directly indicate the value of the measured quantity. An example of this type of environment parameter could be a signal generator.

• A measuring environment variable that influences the measurement process indirectly. An example would be ambient temperature, pressure or humidity that varies from some nominal condition.

± Limits
These are the limits or bounding values that are expected to contain the error in the environment parameter value with some specified containment probability or confidence. These limits may be entered in the table or obtained using the Environment Parameters Tolerance Worksheet.
 
Units
The corresponding units of the ± limits for the environment parameter are entered in this column.
 
Percent Confidence
The probability that the environment parameter error will be contained within the ± limits. 

Deg. of Freedom (or Sample Size)
Either the sample size or degrees of freedom for an environment parameter uncertainty estimate. The choice is made from the Options menu.  The Degrees of Freedom is a statistical quantity that is related to the amount of information available about the uncertainty in the environment parameter error. The degrees of freedom for a Type A uncertainty estimate is equal to the sample size minus one. The degrees of freedom for a Type B uncertainty estimate can be obtained using the Type B Degrees of Freedom Calculator, which can be activated by selecting Deg Freedom on the menu. The Sample Size is number of measurements comprising a sample and is typically used for Type A uncertainty estimates.

Interaction Coefficient
The interaction coefficient is a number indicating the extent to which an environment parameter contributes to the measurement process. The interaction coefficient is expressed in terms of the measurement uncertainty units divided by the environment parameter units.  For example, consider the measurement of the length of a stainless steel pin, with tolerance units of cm. If the environmental factor is temperature, expressed in ºC, then the interaction coefficient is the thermal expansion coefficient for the stainless steel pin expressed in terms of cm / ºC.

Standard Uncertainty
This is the standard uncertainty in a measurement due to a given environment parameter. The standard uncertainty is either computed from the ± Limits and Percent Confidence, or entered directly.

Total Environmental Factors Uncertainty

The bottom section of the Environmental Factors Worksheet displays the total measurement uncertainty due to environmental factors. The uncertainties resulting from the individual environment parameter error sources are combined in a root-sum-square (RSS) manner if none of the errors are correlated.  In some instances, the errors for different environment parameters may be correlated.  If so, the value of the Total Environmental Factors Uncertainty will reflect any correlations between environmental error sources specified by the user.
 
The Degrees of Freedom for the Total Environmental Factors Uncertainty is computed using the Welch-Satterthwaite formula.