m_G: membership to class "gentle"

m_A: membership to class "average"

m_S: membership to class "steep"

If a field has slope 19%, we can use this figure to conclude that it belongs to class "gentle" with membership 0.55 and to class "average" with membership 0.45. (Click here if you want to find out how these numbers were  computed). This agrees with our instictive understanding that a slope of 19% is neither only "gentle" nor just  "average".