A reference sends you to 12v, but the image viewer is already showing page 12. You may not be looking at the same thing. Manuscript references and digital image counters can follow different numbering systems.
Start with the leaf
Getty’s terminology entry describes a folio as an individual leaf, with its sides commonly distinguished as recto and verso. The abbreviations r and v identify those sides.
In a simple illustrative sequence, 12r is followed by 12v, then 13r. That is not the same as numbering every side with a new consecutive page number.
Check the viewer’s labels
A digital collection may include covers, blank leaves or preliminary images in its counter. Record both the manuscript reference and the viewer’s image label when needed. Do not assume image 24 must be folio 12v.
If the catalogue describes multiple numbering systems, preserve that qualification. A neat conversion made without checking can send a reader to the wrong passage.
Write a retrievable reference
Include the holding institution, manuscript identifier, folio and side, plus a stable catalogue link. Add a column or line reference if your source uses one.
The aim is simple: another reader should be able to find what you discussed. Our note on manuscript images and editions explains why locating an image is only the beginning of reading it.