I notice the online manual shows 230 bar as the maximum, maybe this has been updated to 250. The relationship between the maximum and the reg setting is very simple. The maximum is just that, the highest pressure recommended for the rifle. The regulator limits the pressure that is actually allowed to enter the rifle's air plenum, provided the tank/cylinder pressure is at that level or higher. You will probably notice a loss in accuracy at some point under that, depending on range, pellet, etc. So, when the cylinder pressure drops below the reg setting when filled, then it's probably time to top it off. Obviously, the reg pressure will drop when the supply side pressure is less than the reg setting when filled. Since the reg pressure can never be higher than the pressure supplying it, note the reg pressure when you fill the rifle, which will be your benchmark for refilling. And there is nothing wrong with shooting it down below that pressure, some rifles remain accurate for quite a few shots below the regulated pressure. Hope this helps, it sounds more complicated than it is.