For most solids, thermal expansion is proportional to the change in temperature: ε ε t h e r m a l ∝ ∝ Δ Δ T Thus, the change in either the strain or temperature can be estimated by: ε ε t h e r m a l = α α L Δ Δ T where Δ Δ T = ( T f i n a l − − T i n i t i a l ) is the difference of the temperature between the two recorded strains, measured in degrees Fahrenheit, degrees Rankine, degrees Celsius, or kelvin, and α α L is the linear coefficient of thermal expansion in "per degree Fahrenheit", "per degree Rankine", "per degree Celsius", or "per kelvin", denoted by °F, °R, °C, or K, respectively. In the field of continuum mechanics, thermal expansion and its effects are treated as eigenstrain and eigenstress.