Can a second-rate mercury thermometer still be used as a standard?

Yes, but mercury thermometers are dangerous and many countries have adopted bans on them. As early as 1992, Sweden has banned the sale of all medical devices containing mercury. The United Kingdom, France, Denmark and the Netherlands have also banned the use and sale of mercury thermometers. In the United States, 13 states and cities, including San Francisco, Boston and Michigan, have banned the sale of mercury thermometers since 2000. The European Commission has also banned the sale of mercury thermometers since 2005 and banned their export since 2011. According to the Minamata Convention, China will ban the use of mercury thermometers from 2020, less than 2 years from now. Platinum resistance thermometers are safe and reliable and are gradually being recognized by the market, for example, the Zog TM500 portable thermometer can be used as a standard instead of a second-class mercury thermometer.