# Substitution coefficient u

Substitution coefficient for the calculation of the thermal resistance to ambient.

Symbol
$u$
Formulae
 $\frac{2L_{cm}}{D_o}$ Standard case $\frac{2\left(L_{cm}-d_{psc}\right)}{D_o}$ Point source correction $\frac{2\left(L_{cm}+d_{im}\right)}{D_o}$ Non-isothermal earth surface $\frac{2\left(L_{cm}-d_{psc}+d_{im}\right)}{D_o}$ Point source correction & Non-isothermal earth surface
Related
$d_{im}$
$D_o$
$d_{psc}$
$L_{cm}$
Used in
$T_{4iii}$
$T_e$