Before to proceed to the instrument calibration in a DS2500 it is important to check that the instrument is stabilized fine. It is not enough to see that the instrument has pass the diagnostics, yo have to run several times the diagnostics and see that the "deltas" (difference between the nominal and founded values) for the wavelengths checked is stable and it finish drifting due to the warm up of the instrument.
In case that the deltas are close to cero for all wavelengths it is not necessary the calibration with the ERC, but if there is an slope in the values or a systematic difference it is better to calibrate to came with the values close to cero for all the wavelengths.
We don´t want to see drifts in the deltas as the instrument is warming up, and the ideal is to see random differences in the deltas for the several repetitions of the wavelength checks:
At this point we can continue with the calibration of the instrument (video).