### 1.6.4. Algebraic Equations for Additional Variables

Additional Variables may be set up as either algebraic equations or transport equations. For algebraic Additional Variables, you must provide an expression for its value throughout the domain. An algebraic Additional Variable definition can be as simple as a copy of an existing variable.

Important: Results obtained using an Additional Variable that references an existing variable may differ from results obtained using the referenced variable directly. This is because the calculation recipes used for such Additional Variables may differ from those used for the variable referenced. An example of this occurs when the referenced variable is a wall or boundary only variable. In particular, a variable-specific recipe may exist to gather integration point values to nodes and this recipe may differ from the generic recipe applied for Additional Variables.

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