Voltage difference is not the same as potential difference. The potential difference between two points A and B is independent of the path we take from A to B. Therefore in measuring the potential difference between A and B the position of the voltmeter makes no difference. However, it is quite possible for the voltage difference induced between points A and B to depend on the position of the voltmeter, since voltage difference is not a conservative function of position. E.g. consider an infinitely long solenoid using an ac current to generate a varying flux in the interior of the solenoid. Outside the solenoid we have two resistors connected in a ring around the solenoid. The resistor on the left is 100 Ohm and the one on the right is 200 Ohm, they are connected at the top and bottom at points A and B. The induced voltage, by Faraday's law is V, so the current I = V/(100+200). Therefore the voltage across the 100 Ohm resistor is 100I and the voltage across the 200 Ohm resistor is 200I, yet the two resistors are connected on both ends, but Vab measured with the voltmeter to the left of the solenoid is not the same as Vab measured with the voltmeter to the right of the solenoid.