Why would the surface of the cuvette need to be cleaned before taking readings?

The surface of the cuvette needs to be cleaned before taking readings to ensure accurate measurements by preventing any contamination or residue from affecting the light path. Dirt, fingerprints, or scratches can scatter or absorb light, leading to erroneous data. Additionally, a clean cuvette helps maintain consistent optical properties, ensuring reproducibility in experiments. Proper cleaning also minimizes the risk of interference from extraneous substances that could skew results.