An exponential curve fit from Microsoft Excel might not match the exponential curve fit from Spotfire's Lines & Curves feature.

An exponential curve fit from Microsoft Excel might not match the exponential curve fit from Spotfire's Lines & Curves feature.

An exponential curve fit from Microsoft Excel might not match the exponential curve fit from Spotfire's Lines & Curves feature.
  The reason for the difference, when it happens, is that the exponential curve fit in Spotfire's Lines & Curves feature uses nonlinear least squares regression on the original data, and the exponential curve fit in Excel uses linear regression on log-transformed data.

Spotfire is using the direct approach that produces the best fit, and Excel is using an acceptable alternative that produces a "good enough" fit in most cases.