diff --git a/src/edr_pydantic/parameter.py b/src/edr_pydantic/parameter.py
index 1090916..466dbde 100644
--- a/src/edr_pydantic/parameter.py
+++ b/src/edr_pydantic/parameter.py
@@ -12,10 +12,10 @@
 
 
 class MeasurementType(EdrBaseModel):
-    # TODO: Confusion in spec on field name, method versus period.
-    #  See https://github.com/opengeospatial/ogcapi-environmental-data-retrieval/issues/560
     method: str
-    # TODO: Add validation of ISO 8601 duration
+    # TODO: Add validation of ISO 8601 duration (including leading minus sign)
+    # TODO: Confusion in spec on the field name, duration versus period.
+    #  See https://github.com/opengeospatial/ogcapi-environmental-data-retrieval/issues/560
     period: str