diff --git a/.gitignore b/.gitignore
index 022665c..c1b3ec5 100644
--- a/.gitignore
+++ b/.gitignore
@@ -17,3 +17,6 @@ protection*.json
 *.patch
 outputs/*.png
 outputs/*.pdf
+
+# generated metadata (timestamps change on each run)
+data/synthetic/*_meta.json
diff --git a/data/synthetic/fitness_meta.json b/data/synthetic/fitness_meta.json
deleted file mode 100644
index f24a6ec..0000000
--- a/data/synthetic/fitness_meta.json
+++ /dev/null
@@ -1,11 +0,0 @@
-{
-  "seed": 7,
-  "n": 80,
-  "design": "2x2 mixed (Group between \u00d7 Time within)",
-  "programs": [
-    "ProgramA",
-    "ProgramB"
-  ],
-  "dv": "strength_1RM_like",
-  "generated_utc": "2025-11-09T18:46:49Z"
-}
\ No newline at end of file
diff --git a/scripts/ch13_fitness_mixed.py b/scripts/ch13_fitness_mixed.py
index 5eb1491..5127cf3 100644
--- a/scripts/ch13_fitness_mixed.py
+++ b/scripts/ch13_fitness_mixed.py
@@ -1,10 +1,18 @@
 # SPDX-License-Identifier: MIT
-import argparse, os
+import argparse, os, math
 import numpy as np, pandas as pd
 import statsmodels.formula.api as smf
 import matplotlib; matplotlib.use("Agg")
 import matplotlib.pyplot as plt
 
+# --- make Windows console UTF-8 friendly ---
+import sys
+if os.name == "nt":
+    try:
+        sys.stdout.reconfigure(encoding="utf-8")
+    except Exception:
+        pass
+
 def hedges_g(a, b):
     na, nb = len(a), len(b)
     sa, sb = a.var(ddof=1), b.var(ddof=1)