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Scaling Tolerance Variables
For interchange of model data between systems, the "real-world" distance represented by SPAresabs and the actual numeric value of SPAresnor in the two systems should agree. The "real-world" distance refers to an application's interpretation of the numerical value of SPAresabs in conjunction with the assumed units as the distance represented.
For example, two applications may use different numeric values for SPAresabs, but if they assume different units as well, the distance represented by SPAresabs may be the same. If application M uses a unit of millimeters and has a SPAresabs value of 10-6 and application N uses a unit of meters and has a SPAresabs value of 10-9, the "real-world" distance represented by SPAresabs is the same in each application, because 10-6 millimeters = 10-9 meters. The largest dimension represented in each is also equivalent, because SPAresnor does not change. In application M, the largest dimension is 104 millimeters, which is equivalent to the 101 meters representable in application N.
The object transferred should be scaled by the restoring system to maintain the object's original "real-world" size in the restoring system's units. When an object is scaled, the absolute tolerance for which the model is valid is scaled by the same amount.
SPAresabs scaling
To change internal units, only SPAresabs should be changed to reflect the new numerical value of the old "real-world" distance (as represented with the previous units). Even if the application does not need to interchange data, SPAresabs may need to be changed so that the numbers used to represent distances are appropriate for the application. This shifts the dynamic range, but does not change its magnitude.
When different systems share model data, they should agree on the "real-world" distance represented by SPAresabs. This means that they do not necessarily have to agree on the numeric value of SPAresabs, depending on the units being used.
SPAresnor scaling
SPAresnor should not be modified by an application. SPAresnor is a unitless ratio of the smallest number to the largest, and therefore should not be scaled when modifying the unit of measure. The value for SPAresnor needs to be the same between applications that share model data.
Note: If SPAresnor is altered, the behavior of the modeling algorithms is unpredictable.
SPAresfit scaling
There is no inherent requirement for SPAresfit to be equivalent among applications sharing data, because the fit values that are stored with the restored model will be scaled if the model is scaled. For normal operation (fit accuracy and speed), however, SPAresfit should be a reasonable multiple (for example, 1000) of SPAresabs; therefore, if SPAresabs is scaled, SPAresfit should also be scaled.
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