Linear fit in a jumping window

Hi everyone,

What I need to do is a linear fit of a certain part of my dataset. It would work like a window, fitting a certain part of the signal, and then jumps to the next part to fit it, and so on. So I did a loop of polyfit (first order). Does anyone have any suggestions on a simple example?

When I try my code using polyfit (first order) to get coefficients, for each window jump, I get this error (but it works even with this error):

In polyfit at 75
Warning: Polynomial is badly conditioned. Add points with distinct X values,
reduce the degree of the polynomial, or try centering and scaling as described
in HELP POLYFIT.

What do you think this error is trying to tell me?

Thank you.