upgrade/v2106-Developer-Upgrade-Guide.md

@@ -28,6 +28,11 @@
 
 ## Deprecation and Removal
 
+### Deprecated classes
+
+- `partialFaceAreaWeightAMI` : functionality replaced by the faceAreaWeightAMI class.
+- `fieldValueDelta` : equivalent and more flexible functionality offered by the `multiFieldValue` function object.
+
 ### Deprecated Methods
 
 Internal hashing functors have been standardized with method name to