What does a lower numerical value indicate when using a Philadelphia rod?

A lower numerical value on a Philadelphia rod indicates a lower elevation. The Philadelphia rod is an instrument commonly used in the field of civil engineering and site evaluations, particularly when determining the slopes and elevations of land. The readings taken from the rod correlate to specific elevations on a given site. Thus, as the numerical value decreases, it reflects a position that is closer to the datum level or sea level, which signifies a lower elevation.

In contrast, higher numerical values represent higher elevations, as they indicate a position above the established reference point. This fundamental principle is essential for site assessments and helps in the planning and installation of different components of on-site sewage facilities (OSSFs) by indicating how terrain may affect drainage and sewage flow. Understanding this relationship allows installers to make informed decisions about the placement and construction of sewage treatment systems.