${\displaystyle c_{21}=\frac{E_2}{M_1}}$

or

${\displaystyle c_{12}=\frac{E_1}{M_2}}$

Note 1 to entry: The relation between the configuration factor, c, and the (mutual) exchange coefficient, g, is

${\displaystyle {\displaystyle \underset{A_{\text{2}}}{\int }{c}_{\text{21}}\text{d}{A}_{\text{2}}=\frac{{\displaystyle \underset{A_2}{\int }{E}_{\text{2}}\text{d}{A}_{\text{2}}}}{M_{\text{1}}}=\frac{{\Phi }_{\text{2}}}{M_1}=g}=\frac{{\Phi }_{\text{1}}}{M_{\text{2}}}=\frac{{\displaystyle \underset{A_{\text{1}}}{\int }{E}_{\text{1}}\text{d}{A}_{\text{1}}}}{M_{\text{2}}}={\displaystyle \underset{A_{\text{1}}}{\int }{c}_{\text{12}}\text{d}{A}_{\text{1}}}}$

where Φ₂ (or Φ₁) is the flux received over surface S₂ (or S₁) from surface S₁ (or S₂) and A₂ (or A₁) is the area of surface S₂ (or S₁)

Note 2 to entry: The configuration factor has unit one.

Note 3 to entry: This entry was numbered 845-09-72 in IEC 60050-845:1987.