I bet Mrs Beeton used Gas Mk's in her day!I try to be as totally metricated as possible, so I would not normally consider a recipe which used Gas Marks and other, to me, obscure units. Even so, it is nice to know what cubits and ells and Prussian Miles are in modern denominations because one may come across a history book or a cookery book that uses them. This could be a key website for you:
https://www.dovesfarm.co.uk/hints-tips/cheat-sheets
…and here's a taster to help with this evening's supper:
View attachment 558595
BTW My gas oven only has 1 to 9 on the dial..