Simple, really. Abs(x-y) is the difference between the two numbers, absolute, so positive value. So, adding abs(x-y) to the smaller of the two numbers turns it into the bigger number. Plus the bigger number, now you have 2 times the bigger number

For remote backup, always keep your data in multiple ‘importance levels’. There’s replaceable, irreplaceable and very important.

Replaceable is non-niche movies and all kinds of other things that are commonly available, data not ‘exclusive to you’. Irreplaceable is data that is (probably) only owned by you - photos, videos, source code, documents and so on. Very important are the few documents you really can’t afford to lose. Security keys, banking info and so on.

I don’t bother backing up replaceable data - I keep one local and one off site backup for the irreplaceable data and very important data (1tb hetzner storage box is enough for me), and I keep a few encrypted physical usb sticks and sd cards strewn around at my parents and at work for the irreplaceable data that periodically get updated.

At that point, it’s not FOSS, just OSS. Free means that it also uses a license that is ‘Free’ - as RMS would put it ‘libre’. So -, you can - under stipulations, do whatever you want with the Source code.

Definitely. I assume the actual cost for the cable is <10$, but engineering work gets very expensive very fast if you’re small scale.

I’m interested in something - say you got an order for 1 million units, what’s the price per unit you could offer?

Edit: just looked at the DIY option - seems right now you’re just using off the shelf parts, which is fine. Clever use of them, even. Main part seems to be ‘present usb device - once the usb device gets removed, lock down the PC’. So, you specifically just need some usb device with a cord that attaches magnetically - and securely enough that it doesn’t disconnect randomly, with some mechanical way to fix it to yourself. So yeah, at million scale, seems you could definitely sell it for 10 bucks a piece.