Advaith,
DIfference between the ranks of an interval scale is the same, but that doesn't mean you can do ratios among them.
In the case of temperature, it's interval scale, and a temperature reading 10 has the same difference from 20, as it has from 0. But, can't say 20 is double as hot as 10.
Essentially, interval scale can be subjected to subtraction, but only ratio scale can be subjected to division.