Two
Only problem with that as I have seen people take it right to the nth degree running fuel right down to just before low fuel light. That is great but you are relying on your calculation, do you really know how much fuel is in the tank and a gauge that quite frankly should be in Noddy's car. Much better to be a better captain and put it down before things get really out of hand. One should be good at an EOL, maybe not expert for a private pilot but this skill is being gently but deliberetly whittled away by the regulators !