voltmeter

Your diagram shows that point P is at a higher potential than point Q.
If P and Q are connected together (via a resistor, say), there will be a current flowing from P to Q

voltmeter 應該係connect in parallel ga bor.
照你個diagram, 你係咪connect in Series 呢??
咁就measure 唔到個voltage ga la.
但係你係咪想問current 呢??
current 係measured by Ammeter not voltmeter.
而Ammeter 就係connect in series 既.
current in any circuit 永遠都係由 - 去 + 既
所以應該係由Q 去P, 唔係由P去Q

希望幫到你*=]