The line is marked in such a manner that the speed of the current, expressed in knots and tenths, is indicated directly by the length of line carried out by the current pole in a specified interval of time. When marked for a 60-second run, the principal divisions for the whole knots are spaced at 101.33 feet and the subdivisions for tenths of knots are spaced at 10.13 feet. The current line is also known as a log line. An instrument for measuring the speed and direction or just the speed of a current. The measurements are Eulerian when the meter is fixed or moored at a specific location.
Current meters can be mechanical, electric, electromagnetic, acoustic, or combination thereof.
A pole used in observing the velocity of the current. The pole formerly used by the Coast and Geodetic Survey was about 3 inches in diameter and 15 feet long, and was weighted at one end to float upright with the top about 1 foot out of water. Shorter poles were used when necessary for shallow water. In use, the pole is attached to the current line but separated from the graduated portion by an ungraded section of approximately 100 feet, known as the stray line. As the pole is carried out from an observing vessel by the current, the amount of line passing from the vessel during a specific time interval indicates the speed of the current.