Abney level Abney level /ˈeɪbni ˈlɛvəl/

noun

1. A surveying instrument consisting of a spirit level and a sighting tube; used to measure the angle of inclination of a line from the observer to the target  ( Abney level )
   a surveying instrument consisting of a spirit level and a sighting tube; used to measure the angle of inclination of a line from the observer to the target
    Surveyors often use the Abney level to measure land gradients.
   Surveyors often use the Abney level to measure land gradients.