data_map[mapping['tempMaxHourUnit']] = 'C'
     data_map[mapping['tempMinHourUnit']] = 'C'
     data_map[mapping['tempPresUnit']] = 'C'
-    data_map[mapping['precipitationGaugeUnit']] = 'C'
+    data_map[mapping['precipitationGaugeUnit']] = 'mm'
     data_map[mapping['hsUnit']] = 'cm'
     data_map[mapping['windSpeedUnit']] = 'm/s'
     data_map[mapping['windGustSpeedNumUnit']] = 'm/s'
     elif element_cd == 'SNWD':
         value = in_to_cm(value)
     elif element_cd == 'PREC':
-        value = in_to_cm(value)
+        value = in_to_mm(value)
     return value
 
 # CSV operations
     """convert inches to centimetrs"""
     return float(inches) * 2.54
 
+def in_to_mm(inches):
+    """convert inches to millimeters"""
+    return (float(inches) * 2.54) * 10.0
+
 def ms_to_mph(ms):
     """convert meters per second to miles per hour"""
     return ms * 2.236936