diff --git a/hopsflow/util.py b/hopsflow/util.py
index 4999f29..e751e69 100644
--- a/hopsflow/util.py
+++ b/hopsflow/util.py
@@ -117,7 +117,7 @@ class EnsembleValue:
         return EnsembleValue([(N, val[min_index].copy(), σ[min_index].copy())])
 
     def __getitem__(self, index):
-        return EnsembleValue(self._value[index])
+        return EnsembleValue([self._value[index]])
 
     def slice(self, slc: Union[np.ndarray, slice]):
         results = []
@@ -709,7 +709,6 @@ class WelfordAggregator:
             save["tracker"] = self._tracker
 
         with open(path, "wb") as f:
-            portalocker.lock(f, portalocker.LockFlags.EXCLUSIVE)
             portalocker.lock(f, portalocker.LockFlags.EXCLUSIVE)
             np.savez(f, **save)
             portalocker.unlock(f)
@@ -837,7 +836,11 @@ def _ensemble_remote_function(function, chunk: tuple, index: int):
 
 
 def ensemble_mean_online(
-    args: Any, save: str, function: Callable[..., np.ndarray], i: Optional[int] = None
+    args: Any,
+    save: str,
+    function: Callable[..., np.ndarray],
+    i: Optional[int] = None,
+    every: Optional[int] = None,
 ) -> Optional[EnsembleValue]:
     path = Path(save)
 
@@ -860,9 +863,29 @@ def ensemble_mean_online(
         aggregate = WelfordAggregator(result, i)
 
     aggregate.dump(str(path))
+    if every is not None and aggregate.n % every == 0:
+        path.with_stem(f"{path.stem}_{aggregate.n}")
+        aggregate.dump(str(path))
+
     return aggregate.ensemble_value
 
 
+def get_online_values_from_cache(path):
+    path = Path(path)
+    all_versions = list(path.parent.glob(path.stem + "*" + path.suffix))
+
+    final = all_versions[0]
+    all_versions = all_versions[1:] + [final]
+
+    vals = []
+
+    for path in all_versions:
+        agg = WelfordAggregator.from_dump(str(path))
+        vals.append([agg.n, agg.mean, agg.ensemble_std])
+
+    return EnsembleValue(vals)
+
+
 def ensemble_mean(
     arg_iter: Iterator[Any],
     function: Callable[..., np.ndarray],