Like what I make? Want fewer sponsorship ad reads? Consider contributing to my Patreon at https://patreon.com/OurOwnDevices Manufactured in Japan and sold from the 1950s to the 1970s, the Magic Brain was one of the last popular iterations of the slide calculator or "addiator". Invented in the 17th Century and perfected in the 19th, for over 100 years the addiator was a commonplace tool for performing basic arithmetic, operating on an elegant mechanical implementation of the Method of Complements. SOURCES https://americanhistory.si.edu/collections/search/object/nmah_694509 https://www.sliderulemuseum.com/Papers/MagicBrainCalculator.pdf https://www.sliderulemuseum.com/Adders.htm https://www.sliderulemuseum.com/Adders.htm#Addiators http://www.johnwolff.id.au/calculators/addiators/addiators.htm https://www.whipplemuseum.cam.ac.uk/explore-whipple-collections/calculating-devices/pocket-calculating-devices http://www.vintagecalculators.com/html/addiator.html https://www.jaapsch.net/mechcalc/pocket.htm