diff --git a/lib/xmet/thermo.py b/lib/xmet/thermo.py
index 5410411..0dac249 100644
--- a/lib/xmet/thermo.py
+++ b/lib/xmet/thermo.py
@@ -173,7 +173,7 @@ def follow_moist_adiabat(temp: float, pressure: float) -> Series:
 
     return series
 
-def follow_saturated_mixing_ratio(temp: float, pressure: float) -> Series:
+def follow_saturated_mixing_ratio(temp: float, pressure: float, step: float=10.00) -> Series:
     """
     Follow a line of constant saturated mixing ratio calculated from a given
     temp and pressure level, returning a Series object depicting the data
@@ -188,6 +188,6 @@ def follow_saturated_mixing_ratio(temp: float, pressure: float) -> Series:
     while p2 >= PRESSURE_MIN:
         series[p2] = mixing_ratio_temp(ratio, p2)
 
-        p2 -= 10
+        p2 -= step
 
     return series