diff --git a/src/uni2ts/data/builder/simple.py b/src/uni2ts/data/builder/simple.py
index bb54215..c283c54 100644
--- a/src/uni2ts/data/builder/simple.py
+++ b/src/uni2ts/data/builder/simple.py
@@ -14,6 +14,7 @@
 #  limitations under the License.
 
 import argparse
+from collections import defaultdict
 from dataclasses import dataclass
 from itertools import product
 from pathlib import Path
@@ -26,18 +27,19 @@
 
 from uni2ts.common.env import env
 from uni2ts.common.typing import GenFunc
+from uni2ts.data.builder._base import DatasetBuilder
 from uni2ts.data.dataset import EvalDataset, SampleTimeSeriesType, TimeSeriesDataset
 from uni2ts.data.indexer import HuggingFaceDatasetIndexer
 from uni2ts.transform import Transformation
 
-from uni2ts.data.builder._base import DatasetBuilder
-
-
-# Manually set the freq of the datasets whose freq can be inferred automatically.
-freq_dict = {
-    'weather': '10T', 'weather_eval': '10T',
-
-}
+# Manually set the freq of the datasets whose freq can be inferred automatically. Default freq is H.
+freq_dict = defaultdict(
+    lambda: "H",
+    {
+        "weather": "10T",
+        "weather_eval": "10T",
+    },
+)
 
 
 def _from_long_dataframe(
@@ -58,7 +60,11 @@ def example_gen_func() -> Generator[dict[str, Any], None, None]:
             yield {
                 "target": item_df.to_numpy(),
                 "start": item_df.index[0],
-                "freq": pd.infer_freq(df.index) if pd.infer_freq(df.index) is not None else freq_dict[dataset],
+                "freq": (
+                    pd.infer_freq(df.index)
+                    if pd.infer_freq(df.index) is not None
+                    else freq_dict[dataset]
+                ),
                 "item_id": item_id,
             }
 
@@ -92,7 +98,11 @@ def example_gen_func() -> Generator[dict[str, Any], None, None]:
             yield {
                 "target": df.iloc[:, i].to_numpy(),
                 "start": df.index[0],
-                "freq": pd.infer_freq(df.index) if pd.infer_freq(df.index) is not None else freq_dict[dataset],
+                "freq": (
+                    pd.infer_freq(df.index)
+                    if pd.infer_freq(df.index) is not None
+                    else freq_dict[dataset]
+                ),
                 "item_id": f"item_{i}",
             }
 
@@ -123,7 +133,11 @@ def example_gen_func() -> Generator[dict[str, Any], None, None]:
         yield {
             "target": df.to_numpy().T,
             "start": df.index[0],
-            "freq": pd.infer_freq(df.index) if pd.infer_freq(df.index) is not None else freq_dict[dataset],
+            "freq": (
+                pd.infer_freq(df.index)
+                if pd.infer_freq(df.index) is not None
+                else freq_dict[dataset]
+            ),
             "item_id": "item_0",
         }