In 1714, Fahrenheit developed the first modern thermometer — the mercury thermometer, with more refined measurements than previous temperature gauges. Fahrenheit’s thermometer was a take on an alcohol-based thermometer invented by Olaus Roemer, a Danish scientist. Roemer marked two points on his thermometer — 0 as the lowest point, 60 as the temperature of boiling water, 7.5 as the point where ice melted and 22.5 as body temperature. Because the mercury thermometer was more accurate, Fahrenheit decided to expand the Roemer scale by multiplying its values by four. He made adjustments to those metrics based on further research, even putting the thermometer under his wife’s armpit to gain a body temperature.