Modern technology may have provided a great deal of advanced surveying equipment, but simple, “non-electronic” tools are still relevant.
A Philadelphia rod is a type of leveling rod used by surveyors. Made of metal or wood, it consists of two sections, each measured in specific gradients. The two sections are arranged side by side and are joined at one point by a small metal sleeve through which the pieces can slide. This allows the Philly Bar to be used for longer or shorter stretches, allowing it to be functional on a wide variety of terrain types and for increasingly shorter distances. The ability to extend and retract, which also makes it easy to transport, is why the Philadelphia rod is considered by many to be the most popular surveying leveling rod.
Surveying is defined as correctly viewing, measuring, and recording specific positions so that fixed points can be defined for mapping, precise boundaries can be created, and a reading of the grade of terrain can be determined for use in construction. To measure accurately, the survey team needs a fixed observation point, a survey leveling rod held vertically at a second point, and a reading device, much like a telescope combined with a level, with which the surveyor can locate from the first fixed point to the leveling rod.
Philadelphia wood rod construction generally uses maple painted white with black numbers and gradations. Philly metal rods are usually made of aluminum with gradations stamped and also painted black. It is traditional to have a brass sleeve through which the two sections can be slid. In both types of rod construction, extremes of heat or cold can cause the metal or wood to expand or contract and can affect the accuracy of readings.
Philadelphia rods use metric or US standard measurement systems. If metric, the bar is graduated in meters and centimeters, with a bold mark every tenth of a meter point. If measured in feet, the Philadelphia rod is graduated in hundredths of a foot with a bold mark every 10/100 of a foot. The standard Philadelphia bat has two 7-foot (2,134-meter) sections and can be used at a height of 13 feet (3.96 meters).
Philadelphia stem enhancements include removable graduated faceplates. Extensive use over time can wear down and confuse numbers and gradations. Removable faceplates can be replaced as needed to keep graduations visible.