Curve fitting, 2D 3D graph, error propagation, digitizing The LAB Fit is a software for the analysis of experimental data. It has a menu for cuve fitting and the main programs of this menu use nonlinear regression. The LabFit fits functions of one and several independent variables (from 1 up to 6), admitting uncertainties at the dependent variable (Y) and also at the independent variables (X). In case of uncertainties in X and in Y it's made a pre-fit not considering the uncertainties in X, that later on are transferred to Y by propagation of errors. At the LABFit library there are more than 200 functions of one independent variable and almost 280 functions with two independent variables. The user disposes of a finder functions program. If necessary, there is an option so that the user can writes its own fit function. Once determined the fit parameters, it's possible to extrapolate the fit function and, for the 2D and 3D cases, the graph of the obtained function is shown. For the 2D case, beyond the extrapolation possibility, the user can even include error bars and confidence bands to the graph.The LAB Fit has also a menu destined to the treatment of similar data, non-similar data and propagation of errors. Beyond that, there is a third menu with general tools like to plot a function informed by user and many other types of math calculations.And more: the LAB Fit (V 7.2.22 and later) has a reading option used for to extract data from a 2D graph (digitizer for orthogonal and nonorthogonal axes) contained in a graphic file (graph digitizing).Keywords: Curve fitting (fit), least squares, nonlinear regression, treatment of data, basic statistics, errors propagation, 2D and 3D graph, confidence band, uncertainty, error bars, extrapolation, chi-square, correlation coefficient tests, rejection of data, covariance matrix, multivariate, math tools, graph digitizer (digitizing).