HCG levels

So we all know the basics of when you get pregnant your hcg levels go up but I was just curious as to when/how they go up.

I’ve seen some posts say they double every day then some that say that they double every second day?

Also does the double start at conception or at implantation?

If your mom pregnant level has been tested and found at 3 before does that mean it’s always at 3 (non pregnant) or can it go up and down?

TIA ladies xx