So I discovered what is the Game Instance object. It is an object that is persistent during gameplay, in that it stays for the whole duration of the game, then gets destroyed only when the game ends. This makes it much more simple to have data being carried over level loadings in a game that is not using the streaming level system.

Later on you can simply get a reference to it in any script with that node:

First time is use a math expression node in blueprint: 

It basically does the same work than the basic math nodes, but at a reduced cost. I guess its important  to use it when the math is being called in a tick function.

I find it weird that there is nodes to get all basic class instances (Get Game Mode, Get Player Controller, Get Game State)... but not one to get the HUD instance. So I made one:

So I went to a pixel art class...