Non-SI unit of energy. There are three differently defined calories: thermochemical calorie (calth = 4.184 J)
, international steam table calorie (calIT = 4.1868 J)
, 15°C calorie (cal15 = 4.1855 J)
, however only the symbol cal is usually used.
Green Book, 2nd ed., p. 112 (https://dev.goldbook.iupac.org/files/pdf/green_book_2ed.pdf)
PAC, 1996, 68, 957. 'Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)' on page 964 (https://doi.org/10.1351/pac199668040957)