How to find a specific manuscript by shelfmark at the Bibliothèque Nationale Français website

The French National Library has a great mass of medieval manuscripts online at its Gallica site.  Finding them, however, can be very tricky.

Some time back, a genius drew a chart of how to do this.  It does work – my rather Covid-addled memory tells me only that I did work through it. I probably wrote something about it here, but I can no longer locate it.

Today I found a copy of the picture on my desktop.  Unfortunately I don’t know who drew this (if you do, please shout!) and I thought I’d pass it on.  Magic.

How to find a specific manuscript call number BNF.

Update: Nov. 2022.  The step 2 doesn’t work but the department de manuscrits page is here.

Update: August 2023:  The diagram comes from here and was made by “profdiberjones”, @diber.