Magnetic Oil Gauge (MOG) is fixed to the conservator tank of the Transformer to indicate oil level in the conservator tank. The oil levels are generally indicated on the MOG dial as ‘Empty’, 1/4, 1/2, 3/4 and ‘Full’. But in between these levels usually 300C temperature indication is also shown. This is because oil level in the conservator tank changes according to the ambient temperature. The hotter the temperature, the more will be the oil level in the conservator tank due to expansion and vice versa. So, as the oil level depends on the ambient temperature, we must have an indication to what level the oil is to be filled at a certain temperature. This is why the level is indicated in temperature degrees so that the when the ambient temperature is same as the temperature indicated on that MOG dial, the oil level should reach that mark to ensure that the Transformer has sufficient oil level in the conservator. Whenever oil is to be filled in the conservator tank, the level is to be checked properly and to be set according to the ambient temperature prevailing at the time of filling the oil.