# Photometric accuracy in UV/Vis

Hey guys,

I'm calibrating a UV/Vis, instrument model 8453, and I seem to consistently give varying results for the photometric accuracy test (with potassium dichromate).  The protocol requires it be done under 4 minutes.  My question is, why?  Is it unstable?  I'm concerned that the varying pass/fail results could be due to the readings not being done fast enough (?), even if it's under 4 minutes.

Thanks for any info!

B

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