Photometric (absorbance) accuracy is important for many applications of spectrophotometers. Here you can learn more.
Photometric accuracy describes how accurately an instrument can measure the absorbance. It also assures that if the absorbance of a given sample is measured in two different spectrophotometers under identical conditions, the readings will be the same before analysis or any comparison.
Photometric accuracy can be established by measuring solid or liquid filters with known concentrations and absorbance values, and comparing the results with the standard values. A 60 mg / l potassium dichromate (PDC) solution is used for the UV range, and a 0.5 A neutral density filter is used for visible light. The acceptance criteria are the same for both and depend on the absorbance level of the reference material.
Photometric accuracy is quite difficult to achieve due to different instrument designs and optics.
References
1. https://pubs.rsc.org/en/content/articlelanding/2010/ay/b9ay00216b#!divAbstract
2. https://www.agilent.com/cs/library/datasheets/public/a-uvvis05.pdf