Why we use potassium dichromate to calibrate the UV-Spectrophotometer

Why we use potassium dichromate to calibrate the UV-Spectrophotometer .

Potassium dichromate is especially useful in the visible range but also useful in UV. Potassium dichromate itself is stable and avaialble in high purity. In dilute perchloric acid solution, it has a linear response with good temperature stability and also stable as solution. The peaks are well defined, molar absorptivity at 350 nm is accuratly known

Because k2cr2o7 is stable and having high molar mass,
it shows characteristic known wavelengths at 235,257,313 and 430 at specified dilutions!