San Francisco, Oct 7: Twitteratti has its occasional bouts of sad moments but October 2 -- the day when a gunman massacred 59 people and injured several in Las Vegas -- has been recorded as the saddest day on the micro-blogging platform. Using "Hedonometer," a tool that measures happiness on Twitter, researchers have found Twitter users were at their lowest on October 2. According to vox.com, scientists at University of Vermont have been tracking sentiments on Twitter since 2008 with "Hedonometer" which uses an algorithm that scans a random 50 million (or 10 per cent) of all global messages on the microblogging site written in English. It then tracks the most frequently used 10,000 English words on a happiness scale the researchers devised and throws away neutral filler words (like in, and, or of) to arrive at an average measure of our collective joy or sorrow. On their scale of 1 to 9, 9 is termed as "pure happiness" and on an average day, the mood on Twitter hovers around 6 to 6.1. On October 2, the scale dropped down to 5.7. Twitter users were found using very somber words like tragedy, victims, gun, dead, evil, and killed -- words that the algorithm tagged as negative. "It's common for terrorist attacks or natural disasters to move the needle of this instrument, but this is the lowest measurement we've ever had," Chris Danforth, mathematician at University of Vermont, was quoted as saying. "Hedonometer" recordings have shown that people tend to be happier over the weekends (especially Saturdays) and more pessimistic on Mondays and Tuesdays. Thus, the timing of the shooting may have compounded people's sorrow, Danforth added. "It's the biggest mass shooting in [modern] US history, and it happened on one of the days of the week that tend to be sad to begin with," Danforth noted. Further, "Hedonometer" showed that happiness scale is trending down in the past 18 months, especially following the terrorist attacks in Orlando and London and the US election last year. Twitter users seem to be less happy than they were in the last eight years. "[Our happiness cycles have] been incredibly regular for eight years until the last year," Danforth said. "Now the signal is jumping down a lot more, and the regular weekly cycle has fallen apart. It's more of a roller coaster now than it used to be," he added.