Duncan
I am afraid that My experiance of measurements and calculation formula to give wieght of tope was not good.
I carefully took the measurement of a fish that bottomed my [40lb max] scales, to find that the formula gave the weight as 34lb.
The club insists that a fish is weighed, not measured or calculated/estimated
I carry an old mail sack and scales to 110lb should a big one arrive. I have a stainless eye bolted to the back end of the cabin roof to help hold the scales.
if it bottoms those scales it would go back, after photo's of it with a very happy angler.
Charlie