Scale and offset parameters (blue points; a and b terms from Eq. (9)) as a function of time, as determined from fits of the variations of the Stokes U of the reference noise diode with frequency, for PSR J0953+0755. The dashed red lines represent fits of the scale and offset parameters with Gaussian processes. The orange shaded areas represent 95% confidence intervals on the parameter values predicted by the Gaussian processes. Additional details on this analysis can be found in Sect. 3.