diff --git a/fmutool/fmu_container.py b/fmutool/fmu_container.py
index 8ee506c..79214d9 100644
--- a/fmutool/fmu_container.py
+++ b/fmutool/fmu_container.py
@@ -18,11 +18,12 @@ class FMUPort:
     def __init__(self, attrs: Dict[str, str]):
         self.name = attrs["name"]
         self.vr = int(attrs["valueReference"])
-        self.causality = attrs["causality"]
+        self.causality = attrs.get("causality", "local")
         self.attrs = attrs.copy()
         self.attrs.pop("name")
         self.attrs.pop("valueReference")
-        self.attrs.pop("causality")
+        if "causality" in self.attrs:
+            self.attrs.pop("causality")
         self.type_name = None
         self.child = None
 
@@ -52,10 +53,13 @@ def xml(self, vr: int, name=None, causality=None, start=None):
         if causality is None:
             causality = self.causality
 
+        variability = "continuous" if self.type_name == "Real" else "discrete"
+
         scalar_attrs = {
             "name": name,
             "valueReference": vr,
-            "causality": causality
+            "causality": causality,
+            "variability": variability,
         }
         scalar_attrs.update(self.attrs)
 
@@ -173,6 +177,7 @@ def add_vr(self, type_name:str) -> int:
         self.vr_table[type_name] += 1
         return vr
 
+
 class FMUContainer:
     def __init__(self, identifier: str, fmu_directory: Union[str, Path]):
         self.fmu_directory = Path(fmu_directory)