diff --git a/src/derivatives.py b/src/derivatives.py
new file mode 100644
index 0000000..bafaf44
--- /dev/null
+++ b/src/derivatives.py
@@ -0,0 +1,66 @@
+# Copyright (C) 2026 Hector van der Aa <hector@h3cx.dev>
+# Copyright (C) 2026 Pierre Barbier <pierrebarbier741@gmail.com>
+# Copyright (C) 2026 Association Exergie <association.exergie@gmail.com>
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+import argparse
+from pathlib import Path
+
+import pandas as pd
+from tqdm import tqdm
+
+
+def filter_data(file: Path) -> pd.DataFrame:
+    df = pd.read_csv(file, usecols=["time_us", "crank", "cam"])
+
+    crank_df = df.loc[df["crank"] == 1, ["time_us"]].copy()
+
+    crank_df["d1"] = crank_df["time_us"].diff()
+    crank_df["prev_d1"] = crank_df["d1"].shift(1)
+    crank_df["d2"] = crank_df["d1"] - crank_df["prev_d1"]
+    crank_df["ratio"] = crank_df["d2"] / crank_df["d1"]
+
+    crank_df = crank_df.dropna(subset=["d1", "d2", "ratio"])
+
+    return crank_df[["time_us", "d1", "d2", "ratio"]]
+
+
+def main() -> None:
+    parser = argparse.ArgumentParser()
+    parser.add_argument("directory", type=Path, help="Source data directory")
+    args = parser.parse_args()
+
+    directory: Path = args.directory
+
+    if not directory.is_dir():
+        parser.error(f"{directory} is not a valid directory")
+
+    print(f"Processing data in: {directory}")
+
+    concat_files: list[Path] = []
+
+    for path in directory.glob("*.csv"):
+        stem = path.stem
+
+        try:
+            base_name, channel = stem.rsplit("_", 1)
+        except ValueError:
+            print(f"Skipping badly named file: {path}")
+            continue
+
+        if channel != "trimmed":
+            print(f"Skipping unknown file: {path}")
+            continue
+
+        concat_files.append(path)
+
+    for file in tqdm(concat_files, desc="Files"):
+        base_name, _ = file.stem.rsplit("_", 1)
+        output = file.parent / f"{base_name}_derivative.csv"
+
+        out_df = filter_data(file)
+        out_df.to_csv(output, index=False)
+
+
+if __name__ == "__main__":
+    main()