Which expression correctly defines Elevation Factor?

• A. EF = R / (R + H + N)
• B. EF = R / (R + H)
• C. EF = (R + H) / R
• D. EF = R - H

Answer: (A)

Elevation Factor is a proportion that shows how much of the total vertical distance comes from the measured component, compared to the whole vertical stack of components (the measured part plus the instrument height and any additional height offsets). It is defined as EF = R / (R + H + N). This keeps EF as a dimensionless number between 0 and 1, acting as a scale factor when converting or reducing elevations. The idea is that R is only part of the total height you’re accounting for, so you divide it by the full total to get its share. Using alternatives like R/(R+H) ignores N, (R+H)/R inverts the relation, or R − H gives a difference, not a proper proportional factor. That’s why the first expression is the correct definition.