What is an example of an interval variable?

Temperature in Fahrenheit or celcius. In order to be interval, there must be equal distances between equal increments... That is one degree difference must always mean the same thing but zero cannot mean absence. Temperature in Kelvin is ratio because zero means the absence of heat... But not so in other temperature metrics. This is important because 80 is not twice as hot as 40 in most metrics but in Kelvin it is.