[GraemeJ]

Mike, thanks for the quick response. You're right, the initial discussion about incremental backups was nothing to do with restoring a backup to the tablet/s, merely to speed up making the backup.

This all sounds like a lot of additional work for you, with not a lot of gain for the users. I'm probably an unusual case anyway, I doubt many other users are doing quite what I do. Unless you think it really worth the effort, then I'm happy for you to forget all about it.

I tried the Dropbox route, but it is slower. It also eats up my data allowance (I have a satellite link and it's restricted to 25Gb per month).

This house is full of computers!! Three desktop PC's, two laptops and four Android tablets (plus another one that I need to repair) - and there's only two of us here . Other than one of the desktops, which is used for music production and deliberately has no net access whatsoever, all are networked together. I'll have a think about your alternative suggestion.