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!