PS there's another useful app that I bought fro a different purpose, it's called foldersync and comes in free or paid versions. it will let you set up and run a 1 way or 2 way sync between calibre library on a pc ( as a shared folder) and a copy on an SD card. you run it over LAN to sync calibre updates.
https://play.google.com/store/apps/d....full&hl=en_GB
works very well, I was using it to mirror a database of guitarpro scores