In the word use graph does anyone know what the Y-axis represents?
The word usage graph (Ngram) is adapted from books.google.com/ngrams/. It’s a tool that lets you see how often specific words or phrases pop up in books over time, using a massive library of books Google has digitized. When you look at the graph it spits out, the y-axis shows you the frequency of these words or phrases.
The frequency on the y-axis is shown as a percentage, which tells you how many times that word appears compared to the total number of words in books from each year. This number is normalized to appear per million words. So, if you see a frequency of 0.002% in the year 2000, that word showed up about 20 times for every million words in books published that year. This setup lets you fairly compare word usage from year to year, without getting thrown off by years where more or fewer books were published, or the books were just generally longer or shorter. It’s a way to track how language and trends in word usage have evolved over time.