Comparison of parameter estimates from hyperfine fits with SPIF (red histograms; calculations in single precision) and with Scipy optimisation (blue histograms). The histograms are based on synthetic observations with a single velocity component and a relative noise that was varied between 1% and 20% of the peak value in the spectrum. The vertical dashed lines indicate the true values and the initial values used in the optimisation. The bottom frame shows the normalised χ² values for each of the fitted spectra.