The conversion of the Vanguard to the Merchantman incorporated a weight and trim device called STAN, sum total and nose, I think it stood for. You would taxi forward, stop and apply the park brake, then activate the system to check the load sheet. The tolerances were quite high, approximately 2 tonnes for an aircraft with a max take-off weight of 66.5 tonnes. However the system was far more accurate than that.
One winter one of the aircraft was continually just inside the limits. Eventually it was discovered that a drain hole in the fuselage had become blocked and considerably water had pooled which had then frozen.