How can I calculate the slope of third order polynomial fit

I have a third order polynomial fit. I would like to calculate the slope of the fit. Any ideas on how i can do this? Is possible to obtain this from the coefficients?

[p,S] = polyfit(x,y,3);

[y_fit,delta] = polyval(p,x,S);

Answer 1

[John D'Errico]

Is there a reason why you would not think to differentiate it?

help polyder

[Lameck Amugongo]

I would just want to see if the measurement is decreasing/increasing/remaining constant overtime.

for example, [p,S] = polyfit(x,y,1);

p(1) will give the slope of the fit.

How can i get the same slope from high order fit e.g. [p,S] = polyfit(x,y,3); or [p,S] = polyfit(x,y,2);?

Thanks