The Oil Level Indicator (OLI) is developed in response to the need for maintenance professionals to gauge the oil level inside large tanks, gearboxes, and reservoirs. The oil level indicator displays if air bubbles have remained in the transformer. Suppose the gas has generated an internal failure or a leakage at the transformer tank. The indicator's primary purpose is to indicate the oil level inside the tank with a visual hand above the tank.
Oil level indicators can also use in pressurized containers. Pressure test results regarding resistance under pressure are available.