diff --git a/mapies/mapies.py b/mapies/mapies.py
index bc412f73f1fa7205208c0738e5aa0969bfb7c36a..c5a30ced41272ca1d42df34db4c5a0ff003e1d76 100644
--- a/mapies/mapies.py
+++ b/mapies/mapies.py
@@ -364,7 +364,7 @@ class MAPIES:
         # Create xarray Dataset
         ds = xr.Dataset(
             coords={"time": ("time", final_time_seconds, {
-                "units": "seconds since 1900-01-01 00:00:00",
+                "units": f"seconds since {self.time_orig}",
                 "calendar": "gregorian"
             })},