I had this doubt for over 1 year! I thought of asking about it here. In the conversion of a galvanometer to an ammeter by connecting a shunt in parallel to the galvanometer, maximum amount of current flows through the shunt because it has a very very low resistance. In other words, very less amount of current flows through the galvanometer branch. How does it measure the correct current flowing through the circuit? If we connect a normal ammeter in series, all the current flows through it and hence it measure the correct current flowing.