The CalcEngine assembly is separate from the Spread assembly. When a formula is in a cell in Spread, Spread calls the function in that formula and waits for a return of the calculated value. One of the big advantages of offering CalcEngine as a separate assembly, is that you can use the classes for calculating formulas beyond the Spread component.
For an overview of formulas and details on the functions and operators that can be used to create a formula, refer to the Spread for .NET Formula Reference.
For details on the classes in the FarPoint.CalcEngine assembly, which is responsible for the formula calculations, refer to the FarPoint.CalcEngine Namespace and FarPoint.CalcEngine Namespace Inheritance Hierarchy.
See Getting Started.