I'm struggling to understand why 'amps' is a base unit. An amp is defined as one coulomb per second, correct? Then surely it isnt a base unit! It clearly relies on the coulomb. Like, if the coulomb didnt exist, or the amp was discovered before the coulomb was discovered, what would the amp be defined as? Likewise with the coulomb, right... One coulomb is defined as the amount of charge that passes a point in one second when the amphere is one. But the thing is, how can you know what an amphere is if you dont know what a coulomb is? How can you know what a coulomb is if you dont know what an amphere is? Surely one of the units had to have been created first, but how can that be if one cannot exist without the other? I'm just very confused and very frustrated. Ive been thinking about this for days and i still dont get it. Please please could someone just explain to me. It would be very much appreciated.