A moving iron instrument has full scale current of 100 mA. It is converted into a 250V voltmeter by using a series resistance made of a material having negligible resistance temperature coefficient. The meter has a resistance of 320 Ω at 20 °C. After carrying a steady current of 100 mA for a long time, the resistance of the coil increases to 369 due to self heating. When a voltage of 250 V is applied continuously, the error due to self-heating will be nearly.