Two resistance of \( 100\,\Omega \) and \( 200\,\Omega \) are connected in series with a battery of \( 4\,\text{V} \) and negligible internal resistance. A voltmeter is used to measure voltage across \( 100\,\Omega \) resistance, which give reading as \( 1\,\text{V} \). The resistance of voltmeter must be ______ \( \Omega \).