LIke a never-ending yo-yo, this automated tape measure drops a weighted cable to the bulk material surface at timed intervals. AKA plumb bob or bin bob, the SmartBob--by BinMaster-- is highly-reliable and lives a good long service life. SmartBobs can be part of a network connecting multiple vessels and provide inventory control for up to 255 bins of heights up to 150 feet. Made in the USA!