diff --git a/geomagio/residual/Measurement.py b/geomagio/residual/Measurement.py
index c8b44707cf924251de0e7ffa984c1a5cd3cfbc40..e1f98fa5b3065c70eaf3634930809880755dfe4d 100644
--- a/geomagio/residual/Measurement.py
+++ b/geomagio/residual/Measurement.py
@@ -20,6 +20,6 @@ class Measurement(BaseModel):
 
     measurement_type: MeasurementType
     angle: float = 0
-    residual: float = 0
+    residual: float = None
     time: Optional[UTCDateTime] = None
     mask: bool = False