diff --git a/shade_ms/data_mappers.py b/shade_ms/data_mappers.py
index cadee9a..d6b6d16 100644
--- a/shade_ms/data_mappers.py
+++ b/shade_ms/data_mappers.py
@@ -66,15 +66,15 @@ def __init__(self, fullname, unit, mapper, column=None, extras=[], conjugate=Fal
     CHAN  = DataMapper("channel", "", column=False, axis=1, extras=["chans"], mapper=lambda x,chans: chans, const=True),
     FREQ  = DataMapper("frequency", "Hz", column=False, axis=1, extras=["freqs"], mapper=lambda x, freqs: freqs, const=True),
     WAVEL = DataMapper("wavelength", "m", column=False, axis=1, extras=["wavel"], mapper=lambda x, wavel: wavel, const=True),
-    UV    = DataMapper("uv-distance", "wavelengths", column="UVW", extras=["wavel"],
+    uv    = DataMapper("uv-distance", "wavelengths", column="UVW", extras=["wavel"],
                   mapper=lambda uvw, wavel: da.sqrt((uvw[:,:2]**2).sum(axis=1))/wavel),
-    U     = DataMapper("u", "wavelengths", column="UVW", extras=["wavel"],
+    u     = DataMapper("u", "wavelengths", column="UVW", extras=["wavel"],
                   mapper=lambda uvw, wavel: uvw[:, 0] / wavel,
                  conjugate=True),
-    V     = DataMapper("v", "wavelengths", column="UVW", extras=["wavel"],
+    v     = DataMapper("v", "wavelengths", column="UVW", extras=["wavel"],
                  mapper=lambda uvw, wavel: uvw[:, 1] / wavel,
                  conjugate=True),
-    W     = DataMapper("w", "wavelengths", column="UVW", extras=["wavel"],
+    w     = DataMapper("w", "wavelengths", column="UVW", extras=["wavel"],
                  mapper=lambda uvw, wavel: uvw[:, 2] / wavel,
                  conjugate=True),
 )