If the stackup definition includes adjacent parts that have coincident surfaces in the actual assembly but are not correctly aligned in the assembly, Creo Parametric Tolerance Analysis powered by CETOL Technology closes the gaps between them when calculating the stackup nominal. In this scenario, the calculated stackup nominal value is different from the distance between the stackup endpoints measured in the assembly. If you want to include any gaps between parts in the stackup definition, use the Add Offset tool to specify the nominal value of the distance and the associated tolerance.