Everyone knew the world was saddened by the Boston bombings, but now there is proof of that with a Twitter "happiness index" which indicates April 15, 2013 was the saddest day in five years.
The site went online today, and reveals the average emotions of Twitter users in much the say way as the FTSE 100 index expresses economical health.
There are tens of millions of Twitter users all over the world, so the hedonometer can track the emotions of many people.
It works by analyzing words in Twitter updates for "sad," "happy" and "neutral" emotions. Words are assigned a score of 1-9, one being the saddest and nine being the happiest.
Words like "happy," "hahaha," and "cherry" are higher in score than words like "pancake," "and," and "the" which are more neutral. Sad words include "victims, "explosion," "kill," "crash," and "war."
Because many updated their Twitter status to include sad words on April 15, the graph shows a major dip on the day of the bombings.
"Reporters, policymakers, academics - anyone - can come to the site and see population-level responses to major events," Dr. Chris Danfort, one of the mathematicians who developed the site, said.
They have been tracking Twitter users' emotions for five years.
"Many of the articles written in response to the bombing have quoted individual tweets reflecting qualitative micro-stories," Danforth said. "Our instrument reflects a kind of quantitative macro-story, one that journalists can use to bring big data into an article attempting to characterize the public response to the incident."
It is updated every 24 hours, but if they develop it further, it could provide a minute-to-minute update of global happiness.
"We're not trying to tell you that contentment is better than happiness - we're not trying to define the word. We're just saying we're measuring something important and interesting. And, now, sharing it with the world," Danforth said.