Resolution and line spread function (LSF) of the NIRSpec dispersers depend strongly on the light profile of the source. Left: Resolution and corresponding velocity dispersion estimated using our modelling software for a point source in the centre of the shutter and G395H grating (dashed lines). The solid lines show the dispersion curves available on the JWST user documentation webpage (JDox), which provides a (pre-launch) approximation for the LSF of a uniformly illuminated shutter. Right: Ratio of the resolution for a point source and LSF approximation for a uniform light distribution. At shorter wavelengths, the spectral resolution is higher by nearly a factor of 2 for a point source.