Detector tracing for MRS point sources. Top row: detector images of bright star 10 Lac from PID 1524 showing left the IFUSHORT detector (channels 1 and 2), and right IFULONG (channels 3 and 4). Bottom left: single row of detector showing the PSF projected on it and fit with pseudo-Voigt function (inset) to estimate the centre in the detector x (corresponding to α) coordinate. The centre of the trace for the brightest slice (core of the PSF) coincides with the centre of the PSF. Bottom right: collapsed signal over a given number of detector rows in each slice is fitted with a pseudo-Voigt profile to estimate the across slice coordinate s (equivalent to β).