Interval Scales of Measurement

On an interval scale, measurements are not only classified and ordered therefore having the properties of the two previous scales, but the distances between each interval on the scale are equal right along the scale from the low end to the high end.

Two points next to each other on the scale, no matter whether they are high or low, are separated by the same distance, so when you measure temperature in centigrade the distance between 0 and 10°C is the same as between 90 and 100. What you must remember though is that for interval scales, a measurement of 100°C does not mean that the temperature is 10 times hotter than something measuring 10°C even though the value given on the scale is 10 times as large.

That's because there is no absolute zero, the zero is arbitrary. On the centigrade temperature scale, the zero value is taken as the point at which water freezes and the 100°C value when water begins to boil and between these extreme values the scale is divided into a 100 equal divisions.

Temperatures below 0°C are designated negative numbers. So the arbitrary 0°C does not mean 'no temperature'. But when expressed on the kelvin scale, a ratio scale, a measure of 0K equivalent to -273°C does indeed mean no temperature!

Calendar years are another example of an interval measurement. An arbitrary 0 (or 1 depending on your viewpoint) was assigned when Christ was born, and time before this is given the prefix BC. Other than these examples interval measurements are rare.