# What are Tetens coefficients?

Tetens coefficients appear in a few meteorological/climatological models that I've been looking at,for example APSIM:

svp_A = 6.106
svp_B = 17.27
svp_C = 237.3


These same values appear in at least two other models, but I can't find any documentation about what they represent, or where they come from. What are these numbers?

Edit: Oroud, I. M., 2001, Dynamics of evaporation from saline water bodies uses these constants and references Tetens, O. 1930 "Uber einige meteorologische Begriffe." Z. Geophys. 6: 297-309, but that text doesn't appear to be available online, or in my university's library.

$$e_s(T)= 6.1094 \exp \left( \frac{17.625T}{T+243.04} \right)$$