diff --git a/geomagio/StreamConverter.py b/geomagio/StreamConverter.py
index a51751444367ba838b35c092be8826ac02ef9c9f..7629c00d4a2d705ab3d0ec1bf6712eea9d1a16b3 100644
--- a/geomagio/StreamConverter.py
+++ b/geomagio/StreamConverter.py
@@ -55,6 +55,18 @@ def get_geo_from_obs(obs):
 
 
 def get_mag_from_geo(geo):
+    """Convert a stream to magnetic coordinate system.
+
+    Parameters
+    ----------
+    geo: obspy.core.Stream
+        stream containing observatory components X, Y, Z, and F.
+
+    Returns
+    -------
+    obspy.core.Stream
+        new stream object containing magnetic components H, D, Z, and F.
+    """
     x = geo.select(channel='X')[0]
     y = geo.select(channel='Y')[0]
     z = geo.select(channel='Z')[0]