Detect sludge in your container; an alarm sounds when the indicator comes into contact with sludge. Unwind the cable from the hand-held spool to lower the indicator into your liquid and press the trigger. The alarm’s pitch and volume will increase with sludge thickness. Calibrate the indicator with a sensitivity control; it can be set high enough to sound the alarm when the probe encounters even slightly cloudy water. Use the marking decals to mark the cable in foot or meter increments.