DataFitX is a COM component (in-process ActiveX DLL) which allows you to add a powerful nonlinear regression (curve fitting) engine to your software with just a few simple lines of code. DataFitX is developed using COM, so it can be used in any environment that supports COM, including Microsoft Visual Basic, Microsoft Visual C++, Delphi and VBA (Microsoft Excel, Microsoft Access or any VBA enabled client). A DataCollection object provides methods and procedures for importing and gathering data, as well as providing statistical summaries for the data. The NonlinearRegression and MultipleNonlinearRegression objects provide methods and procedures for defining regression models with up to 100 fitting parameters and performing nonlinear regression on data containing up to 50 independent variables. The CubicSpline object performs cubic spline interpolation on 2-dimensional data. These objects provide properties and methods that return results for the fitting parameters, as well as detailed statistical summaries of the regression results. Arrays of predicted values and residuals are automatically generated, but you can also predict values on a point by point basis (Y at a value of X), or create arrays of predicted values based on data arrays you supply. These objects also include methods to perform derivative and multiple root calculations (X values at a specified value of Y). There are more than 600 pre-defined models, but you can easily define your own by passing a string representation of a model to one of the model creation methods. You can also create event-based regression models, which allows the client code to supply the function evaluations and optionally the derivative calculations through raised events. There are ten objects with 232 methods, procedures and events. You can process the regression results in the client code, or export regression results in DataFit native file format. A DataFitX developer license includes royalty free run-time distribution.