The Nominal Build command sets all points within the model to their nominal positions, then assembles all the parts of the model using all active Moves.  All moves will be performed in one step and the parts will be considered to be in Nominally built position. The parts must be Nominally Built in order for a Monte Carlo analysis, Contributor Analysis or GeoFactor Equation-Based analysis to see the effects of the assembly buildup variation.  The Nominal Build icon can be found in the Analysis Toolbar.

In contrast, Assemble will only perform all active Moves within the model without resetting DCS Point and entity locations.