Spectral scans of atomic line emission sources with a Shimadzu UV2101PC spectrophotometer show that the nominal wavelength depends upon the instrumental slit width, the wavelength sampling interval, and for some slit widths, also on the specified spectral range. The range dependence is manifested as a smoothing that occurs when the range includes >65 sampled wavelengths, and it affects both the wavelength and the line shape. For spectra not subject to this smoothing, the wavelength error looks like a one-sample misassociation of the wavelength and photometric readings. However, the instrument does reliably move to a specified wavelength, independent of the scan parameter settings. These behaviors do not seem to be documented anywhere but have been present in the software for operating this instrument for about two decades.
Joel Tellinghuisen, "Wavelength Anomalies in Ultraviolet-Visible Spectrophotometry," Appl. Spectrosc. 66, 1362-1364 (2012)