diff --git a/lib/xmet/hodograph.py b/lib/xmet/hodograph.py
index 15fee0e..79cc4d1 100644
--- a/lib/xmet/hodograph.py
+++ b/lib/xmet/hodograph.py
@@ -1,7 +1,7 @@
 import math
 import cairo
 
-from xmet.igra     import IGRAReader
+from xmet.units    import rad, knots
 from xmet.sounding import Sounding
 
 WIND_SPEED_MAX  = 140 # knots
@@ -10,15 +10,6 @@ WIND_SPEED_STEP =  10
 
 WIND_DIR_STEP = 30 # degrees
 
-def radians(degrees: float) -> float:
-    return (degrees + 90) * (math.pi / 180.0)
-
-def degrees(radians: float) -> float:
-    return (radians * (180.0 / math.pi)) - 90
-
-def knots(ms: float) -> float:
-    return ms * 1.944
-
 class Hodograph():
     def __init__(self, width, height):
         self.width   = min(width, height)
@@ -29,8 +20,8 @@ class Hodograph():
     def sample_to_screen(self, wind_speed: dir, wind_dir: float) -> tuple:
         r = self.radius * (wind_speed / WIND_SPEED_MAX)
 
-        x = self.radius + r * math.cos(radians(wind_dir))
-        y = self.radius + r * math.sin(radians(wind_dir))
+        x = self.radius + r * math.cos(rad(wind_dir))
+        y = self.radius + r * math.sin(rad(wind_dir))
 
         if self.extents is None:
             return x, y