Back when I was an apprentice many many years ago one of my tasks was to make wedding ring blanks. A boring task but made easier with the help of an old hand written chart with calculations of the length of metal needed to make a particular size. You just had to look down the list to the size you wanted ( lets say P for the sake of example ) read the length of metal ( lets say 60mm ) add the gauge of the metal then just saw it off. It was a great thing to have but I no longer have it and the man who I got it from is long gone. Does anyone on here have such a thing?