diff --git a/lib/xmet/thermo.py b/lib/xmet/thermo.py
index b15cc83..380cf57 100644
--- a/lib/xmet/thermo.py
+++ b/lib/xmet/thermo.py
@@ -11,11 +11,19 @@ def saturated_vapor_pressure(temp: float) -> float:
         (7.5 * temp) / (237.3 * temp)
     )
 
+"""
+Return the amount, in grams, of water vapor versus dry air in a parcel of a
+given dewpoint and pressure.
+"""
 def mixing_ratio(dewpoint: float, pressure: float) -> float:
     e = vapor_pressure(dewpoint)
 
     return 621.97 * (e / (pressure - e))
 
+"""
+Return the maximum amount, in grams, of water vapor a parcel of a given
+temperature and pressure can hold.
+"""
 def saturated_mixing_ratio(temp: float, pressure: float) -> float:
     es = saturated_vapor_pressure(temp)