Quoting convention for Gold in the early 1900s I was looking at some historical references on gold prices over the past century and I noticed that London gold prices are written as "$x$ s. $y$ d" (e.g., '$121 \text{s}. 1.75 \text{d}$'). I'm wondering how I'd go about converting this into pounds. Thanks!
Have you considered googling the subject? 
By doing so I have found: 
https://en.wikipedia.org/wiki/%C2%A3sd 


  £sd (occasionally written Lsd) is the popular name for the pre-decimal currencies once common throughout Europe, especially in the British Isles and hence in several countries of the British Empire and subsequently the Commonwealth. [...] In the classical Roman Empire, standard coinage was established to facilitate business transactions. 12 denarii were rated equal to 1 gold solidus – a 4th-century Roman coin that was rare but which still circulated; and, since 240 denarii were cut from one Roman libra of silver 240 denarii, therefore, equalled one pound (livre in France, peso in Spain, etc.). [...] Different monetary systems based on units in ratio 20:1 &amp; 12:1 (L:S &amp; S:D) were widely used in Europe in medieval times. The English name pound is a Germanic adaptation of the Latin phrase libra pondo 'a pound weight'. [...] In writing, there were several conventions for representing amounts of money in pounds, shillings and pence: £2.3s.6d. (two pounds, three shillings and sixpence)