Have just been reading Horace Ford's Victorian treatise on Archery

(much to my daughter's annoyance, claims I'm addicted!). Horace says Gents' arrows should be between 4s 3d and 5s 6d in weight. According to my dictionary a "pennyweight" is 1/20 of an ounce (Troy), meaning that he is suggesting weights of between 2 and 11/20ths and 3 and 4/10ths ounces? (I think I remember that there were 12 pennies in a shilling?) (He also suggests draw weights of 48 to 63 lbs for Gents, surely too low for such hefty arrows?). That seems pretty heavy arrows to me! I shoot a 53lb bow and my arrows weigh between 1 and 1.2 ounces. Given the rule of thumb of "10 grains per pound of draw weight" I have seen elsewhere on the forum I think that is about right?
I am sure I must have this utterly round my neck at some point and am hoping somebody can politely point out my mistake?