Editing Cetane number (section)

===Cetane index===
{{Main|Cetane index}}
Another statistic used by fuel-users to control quality is the cetane index (CI), which is a calculated number based on the [[density]] and a distillation range of the fuel. There are various versions of this, depending on whether metric or Imperial units are used, and the number of distillation points that are used. These days most [[petroleum industry|oil companies]] use the '4-point method', ASTM D4737, based on density and 10% 50% and 90% recovery temperatures. The '2-point method' is defined in [[ASTM]] D976 and uses just density and the 50% recovery temperature. This 2-point method tends to overestimate the cetane index and is not recommended. Cetane index calculations cannot account for cetane improver additives and therefore do not measure the total cetane number for additized diesel fuels. Diesel engine operation is primarily related to the actual cetane number, and the cetane index is merely an estimation of the base (unadditized){{clarify|date=October 2023}} cetane number.