Hemoglobin can be measured manually using a spectrophotometer or colorimeter. Bathochromic shift is typically demonstrated using a spectrophotometer, colorimeter, or spectroradiometer. Internally the meter is typically a silicon photodiode tristimulus colorimeter. The equipment required is a colorimeter, some cuvettes and a suitable color reagent. The College of Optometrists (UK) has specified guidelines for optometrists who use the colorimeter system. The quality of a colorimeter may be assessed using the means in CIE publication 179&colon;2007. The concentration of a colorless solution cannot normally be determined with a colorimeter. In a manual colorimeter the cuvettes are inserted and removed by hand. The filter on a colorimeter must be set to red if the liquid is blue.