The source data was Google's web n-grams database which is released by Google under the Creative Commons Attribution 3.0 Unported licence.

I created the two graphical curves with Google's ngram viewer archive copy at the Wayback Machine which generates a bitmap output. With Inkscape, I extracted the two curves from the bitmap and converted them to vector-objects, then I manually re-drew the grid and legends.

I set the ngram viewer to show the incidence of the words "laſt" and "last" in all English documents (including British and American) from 1700 to 1900. I actually entered the words "laft" (with a small-F) and "last" because Google's OCR technology misread the long-s as an "f". This has been corrected by Google since the creation of this picture, so to be able to make a distinction between the two kinds of "s", one has to select one of the 2009 corpora.

The ngram viewer allows the user to examine a sample of documents that were referenced by the search with the target words highlighted. I saw that the apparent minor peaks of short-s usage during 1700-1800 were largely not due to actual short-s usage, but due to the occasional use of a different OCR technology that was able to recognize the long-s as an "s" rather than an "f". This was particularly noticeable when the ngram viewer was set to look at American documents only, which gave unusably uneven curves from 1700-1800, partly because there are not enough American documents from that period to form smooth curves, and because of the usage of the better OCR on about one-third of the American documents from that period.

Data from Google used to create this diagram:

Aquest fitxer està subjecte a la llicència de Creative Commons Reconeixement 3.0 No adaptada.

Sou lliure de:

• compartir – copiar, distribuir i comunicar públicament l'obra
• adaptar – fer-ne obres derivades

Amb les condicions següents:

• reconeixement – Heu de donar la informació adequada sobre l'autor, proporcionar un enllaç a la llicència i indicar si s'han realitzat canvis. Podeu fer-ho amb qualsevol mitjà raonable, però de cap manera no suggereixi que l'autor us dóna suport o aprova l'ús que en feu.

https://creativecommons.org/licenses/by/3.0CC BY 3.0 Creative Commons Attribution 3.0 truetrue

With the proviso that the source data was licensed as Creative-Commons, I release the diagram itself as PD:

Jo, el titular del copyright d'aquesta obra, l'allibero al domini públic. Això s'aplica a tot el món. En alguns països això pot no ser legalment possible, en tal cas: Jo faig concessió a tothom del dret d'usar aquesta obra per a qualsevol propòsit, sense cap condició llevat d'aquelles requerides per la llei.