A circuit consists of an ideal power supply of emf \(\mathcal{E} = 24\text{ V}\) connected in series with resistors \(R_1 = 12\text{ k}\Omega\) and \(R_2 = 20\text{ k}\Omega\). A non-ideal voltmeter with an internal resistance of \(R_V = 30\text{ k}\Omega\) is attached in parallel across \(R_2\). What is the absolute difference between the potential difference across \(R_2\) before the voltmeter was connected and the reading displayed on the voltmeter?