Why is it called a ratio scale? Can you provide a simple example that clearly explains- why ratio scale is called ratio scale?

In an interval scale, the intervals are equal.
The increase in temperature from 10 degrees to 20 degrees is the same increase from 20 degrees to 30 degrees. The intervals are equal. That's not true for a scale of, say math ability. Is the difference in math ability between someone who scores 10 and someone who scores 20 the same as the difference in math ability between someone who scores 20 and someone who scores 30? What does 10 more points of math ability even mean?
But in a scale that's not ratio, the ratios don't make sense. You can't double 10 degrees and get 20 degrees, and call that twice as hot.
In a ratio scale, ratios make sense. 20lbs is twice as much mass as 10lbs. 1 minute is half of 2 minutes. (And if you're using temperature, you can use the Kelvin scale, which does have a true zero, and is ratio).
