declination vs gradient

declination

noun
  • At a given point, the angle between the line connecting this point with the geographical center of the earth and the equatorial plane. 

  • At a given point, the angle between magnetic north and true north. 

  • A refusal. 

gradient

noun
  • A slope or incline. 

  • The ratio of the rates of change of a dependent variable and an independent variable, the slope of a curve's tangent. 

  • A differential operator that maps each point of a scalar field to a vector pointed in the direction of the greatest rate of change of the scalar. Notation for a scalar field φ: ∇φ 

  • A gradual change in color. A color gradient; gradation. 

  • The rate at which a physical quantity increases or decreases relative to change in a given variable, especially distance. 

  • A rate of inclination or declination of a slope. 

adj
  • Adapted for walking, as the feet of certain birds. 

  • Moving by steps; walking. 

  • Rising or descending by regular degrees of inclination. 

How often have the words declination and gradient occurred in a corpus of books? (source: Google Ngram Viewer )