Hi,
I think it would be great if the Calibre tool had a diff view, where you could see which books in your library are not on your device.
Or perhaps a new column (On Device [Y/N]) where you could filter a search by or at least sort.
If this request has been suggested before my apologies but please add one vote from me.
Thanks
PS: Great software!, UI needs to be a little more responsive tho
Guido