Simple Level Measurement

 Sight Glass

Sight glass is direct method to measure level. Only local indication is possible by this method.

If a scale is placed near the sight glass we can measure the level of  a tank. Isolation valves should place in between the sight glass and tank, in both ends.
Isolation valves will help to isolate both ends of the tank(connected to sight glass) during maintenance of the  sight glass (replacement). If the glass is broken leakage of the fluid in the tank can be isolated by the isolation valves.

Float and Tape