When you apply a curve fit and extrapolate to the axis limits, the values you obtain from the fit will only be valid across the range of X that is either displayed or included in the original data. Beyond this range, the values are linearly interpolated. The extrapolate feature in KaleidaGraph will not calculate values beyond what is displayed in the plot.
KaleidaGraph is a thoughtfully designed graphing and data analysis application for research scientists, as well as for those in business and engineering fields. It produces publication-quality graphs, and easily converts the most complex data into a functional display.