Method for calibrating an apparatus for measuring the absorbance of light by a substance

A computer implemented method performed by a computer configured to calibrate an apparatus for measuring absorbance of light of a substance for a chromatography system, the apparatus comprising a conduit for enabling a fluid to be measured, a light emitter configured to emit light along an optical path to a light sensor configured to measure the emitted light, the optical path intersecting the conduit, a rotating disc having one or more optical filters, each of the one or more optical filters is arranged with its center passing through the optical path when rotating, an actuator configured to rotate the disc dependent on a control signal, the method comprising:

• controlling rotation of the disc to a first position where a first filter, of the one or more optical filters, intersects the optical path at a first point,
• measuring a first light absorption value,
• controlling rotation of the disc to a second position, different to the first position, where the first filter still intersects the optical path at a second point,
• measuring a second light absorption value,
• generating an aggregated light absorption value, and
• calibrating the apparatus by comparing the aggregated light absorption value to a reference light absorption value.