According to the Buckingham π–Theorem, the number of independent dimensionless groups, formed by combining the physical variables of a problem, is equal to

• A. [total number of physical quantities (n)] – [the number of primary dimensions (m) needed to express the dimensional formulae of n physical quantities]
• B. [the number of primary dimensions (m) needed to express the dimensional formulae of n physical quantities] – [total number of physical quantities (n)]
• C. [the number of primary dimensions (m) needed to express the dimensional formulae of n physical quantities] + [total number of physical quantities (n)]
• D. [the number of primary dimensions (m) needed to express the dimensional formulae of n physical quantities] x [total number of physical quantities (n)]