Is the degree of absoluteness of zero the only difference between interval scale and ratio scale? What does it mean when you say a thing has no absolute zero? Is it just that zero is another measurement unit in the interval scale? Do we represent and measure data differently using interval and ratio scales? They often say you can't say that temperature today is twice the temperature it was the day before, but no one tells us why? The following statement is what I found in an article;
"Since the interval scale has no true zero point, you cannot calculate Ratios. For example, there is no sense the ratio of 90 to 30 degrees F to be the same as the ratio of 60 to 20 degrees.
A temperature of 20 degrees is not twice as warm as one of 10 degrees." Is there any specific reason?
"Thus, the interval scale only allows you to see the direction and the difference between the values, but you can not make statements about their proportion and correlation." What do they mean when they say no statement about their proportion and correlation?
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$\begingroup$You can divide $40$ degrees Celsius by $20$ degrees Celsius and get $2$. But that number is meaningless. That's so because $40$ degrees Celsius is equal to $104$ degrees Fahrenheit and $20$ degrees Celsius is equal to $68$ degrees Fahrenheit. But $\frac{104}{68}\ne2$.
On the other hand, if, say you measure two speeds in kilometers per hour and also in miles per hour, the quotients will be the same in both cases. Se, here, to say that a speed is, say, $20\%$ greater than another speed (that is, the quotient is equal to $1.2$) has a meaning, since it does not depend upon the units that you have chosen.
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