This site presents the history of the slide rule in France in the 19th century. Indeed, it was between 1815 and the end of this century that French manufacturers dominated the manufacture of this instrument. and made decisive improvements that will last until the end. This period has little been studied and it seems to me that it deserves to be better known.
You will also find the rules, mainly French ones, of my collection representative of this time.

For a more detailed study, see my book
"La règle à calcul, la longue histoire d'un instrument oublié", Presses universitaires de Limoges, 2018. (in French)