Although the dipstick and lead line method of level measurement are unrivalled in accuracy, reliability, and dependability, there are drawbacks to this technique. First, it requires an action to be performed, thus causing the operator to interrupt his duty to carry out this measurment. There cannot be a continuous representation of the process measurement.
Aother limitation to this measuring principle is the inability to successfully and conveniently measures level values in pressurised vessels.
These disadvantages limit the effectiveness of these means of visual level measurement.
Sight Glass: