A pole, usually made of varnished hardwood, that is inserted into a liquid fuel storage tank to measure the amount of product it contains.
Numbers, calibrated to 1/8 inch, are embossed along the side of the gauge stick. After inserting the stick in the tank, the operator withdraws it and notes how far up on the numbers the "wetness" has extended. By referring to a tank conversion chart, he can convert the number of wetted inches indicated on the stick to the number of gallons remaining in the tank.
A station operator, concerned about the possible presence of a layer of water on the bottom of a storage tank, can use his gauge stick to check for water. He does this by smearing a compound called water-finding paste on the lower end of the stick before he inserts it into the tank. If water is present, the paste will change color, revealing not only the presence of water on the tank bottom but its depth, as well. A special paste must be used for alcohol-blended gasolines.
See also Water finding paste.