To meet 2nd Order specifications, which leveling staff specifications are required?

• A. Philadelphia style leveling staff with temperature expansion coefficient 10 ppm/°C or less
• B. Plastic staff
• C. Digital staff with 50 ppm/°C
• D. Metal staff with no expansion data

Answer: (A)

For 2nd order leveling, controlling the effect of temperature on measurements is essential because even small changes in staff length can introduce noticeable errors. The leveling staff you use must have a very small temperature expansion so that readings stay stable as temperature varies. A Philadelphia style leveling staff with a temperature expansion coefficient of 10 ppm/°C or less provides a near-minimal change in length with temperature, which helps keep the error terms within the tight limits required for 2nd order accuracy. Other options are unsuitable because a plastic staff generally expands more with temperature, a digital staff with 50 ppm/°C still has too much expansion to meet the stringent 2nd order tolerance, and a metal staff without documented expansion data cannot be corrected for temperature effects, leaving unresolved error sources.