There's a difference in the dials on Weston US and Weston Europe.
If I set my Weston original, or my Weston II to Weston 80 and point the dial at 400, I get f16 at 1/150.
If I set them to 64, I get f16 at 1/130. If I imagine nudging the dial slightly to the left of 400, I can imagine a reading of 1/125.
So 381 is scientifically accurate, 400 is close. These should agree with Sunny 16. No chart required.