Instead of concerning with actual numbers for comparison, it is sometimes easier to pick a zero point off an average and then use standard deviation to determine the variance in data. A value such as this would be called an index as it is a reference tool for all data to be translated off of. This is especially useful in comparing change over time in any type of numerical data, including natural phenomena and economic growth or recession. This map here shows the ice melting data from Antarctica that has been indexed to represent a trend over time. The SOI dots represent the conditions of the Southern Oscillation—famously called El Niño—and the SAM dots represent the Southern Hemispheric Annular Mode which is a measure of pressure changes between the Southern Hemisphere's high and middle latitudes. This indexing shows simply that the melting index drops into a negative rate once the SOI and SAM index rates begin to rise—this is an important and interesting correlation.
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