Update app.py

app.py

@@ -107,7 +107,7 @@ def compute_mm_per_pixel(path):
         return (1.0 / tick), "tickmarks"
 
     # C) Fallback 300 DPI
-     return 0.056, "fallback"
+     return (25.4 / 453.5714), "fallback"
 
 
 # ==========================