PREVIOUS button

PREVIOUS button

I'm doing edits in Develop module.  When going onto the next image, I can't see the 'PREVIOUS' button, to apply last image's edits.  I only see SYNC and RESET buttons in that position.

Is this anything to do with how/where images have been imported from (e.g. 'PREVIOUS' won't work with tethered capture vs imported TIFFs)?

Thanks