<https://sciencing.com/calculate-proportionality-6076375.html>
<http://schema.org/description>
"The term \"proportionality\" means a ratio between two quantities that does not vary -- that is, the ratio remains constant. Proportionality is an extremely useful concept. For example, suppose a small plane pilot knows his aircraft gets 10 miles for each gallon of fuel consumed. The ratio is thus 10 miles per gallon. If the pilot knows how many gallons of fuel the plane will carry, he can calculate how far the plane can be flown safely."
<https://sciencing.com/calculate-proportionality-6076375.html>