How do you work out gear ratios

enjoy your drugs-reefers, but I hope you don't do it too long and end up like those twitchy, bedraggled weirdy-beardy old stoners (who carried on smoking after all their friends gave up and started playing golf and cleaning their cars) who constantly mutter, bitterly, about conspiracy theories and "them" then stick silver foil over the electrical sockets in case "they" get "in"

To be fair, that sounds a lot better than playing golf.