A Philadelphia rod is a

level staff {{short description, Graduated rod used to measure differences between heights A level staff, also called levelling rod, is a graduated wooden or aluminium rod, used with a levelling instrument to determine the difference in height between points ...

used in

surveying Surveying or land surveying is the technique, profession, art, and science of determining the terrestrial two-dimensional or three-dimensional positions of points and the distances and angles between them. A land surveying professional is ca ...

. The rod is used in

levelling Levelling or leveling (American English; American and British English spelling differences#Doubled in British English, see spelling differences) is a branch of surveying, the object of which is to establish or verify or measure the height of sp ...

procedures to determine

elevation The elevation of a geographic location is its height above or below a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface (see Geodetic datum § Vert ...

s and is read using a

level Level or levels may refer to: Engineering *Level (instrument), a device used to measure true horizontal or relative heights *Spirit level, an instrument designed to indicate whether a surface is horizontal or vertical *Canal pound or level *Regr ...

. A Philadelphia rod consists of two sliding sections graduated in hundredths of a foot. On the front of the rod the graduation increasing from zero at the bottom. On the back of the rod the graduation decrease from 13.09 ft at the bottom to 7 ft. The division of the device in two sliding sections are devised for ease of transport. Readings of or less, and up to , can be measured. It has a rear section that slides on the front section. The rod must be fully extended, when higher measurements are needed to avoid reading errors. Distances of up to may be read. File:Reading Leveling Rod jpeg.png, Reading a Philadelphia rod File:Leveling Rod reading examples jpeg.png, Philadelphia rod reading examples The rod may be equipped with a target to increase the readable range of the rod. When the target is equipped with a

Vernier scale A vernier scale, named after Pierre Vernier, is a visual aid to take an accurate measurement reading between two graduation markings on a linear scale by using mechanical interpolation, thereby increasing resolution and reducing measurement unce ...

measurements to the thousandths of a foot are possible. For readings less than 7 ft the target is attached on the bottom section of the rod and adjust by signals from level operator until the target is inline with the level's horizontal cross hair. For readings greater than 7 ft the target is attached to top section of the rod and the top section is raised/lowered until it the target intersects with the cross hair of the level. The rod is then locked and the zero of Vernier scale on the back of the rod will be aligned with the target's height.

References

{{Reflist Surveying instruments