Mask effectiveness scale Posted on 2020-10-03 by Frederick Calica Mask effectiveness scale Masks https://t.co/eD8TjYbNs2 https://t.co/7Ezbi4ttn1 pic.twitter.com/L77HiJ2Qw6— XKCD Comic (@xkcdComic) October 2, 2020 Originally tweeted by Frederick Calica (@icheb) on 3 October 2020.