Why is mercury thermometer most accurate to measure fever?

Mercury-in-glass thermometers have been considered the most accurate liquid-filled types (Source: http://en.wikipedia.org/wiki/Medical_thermometer) and therefore used with confidence in home or clinics all over the world. It may be assumed that accurate measurement of fever (body temperature) is vital in deciding correct course of treatment. People who have used mercury fever thermometer ever in their lifetime do not (wouldn't) like to use any other type (read digital thermometer) of thermometer because they have been so used to the accuracy of mercury thermometers.

The governments of few countries have been advocating ban on these mercury filled thermometers because mercury is considered 'toxic' heavy metal and also not good for environment but experts believe that fever thermometers have such a low amount of mercury that even if the thermometer breaks and mercury is spilled over, it rarely pose any danger of any kind. One of the Doctor who still use a mercury fever thermometer once asked me that how many times I have broken or ever seen a broken mercury thermometer and my answer was 'never'. With little care and attention, one can keep these accurate mercury fever thermometers at home for years and years.

Despite being the poorest conductor of heat mercury is still used in thermometers because of the fact that it is the only one metal that remains in liquid state at room temperature and has a high coefficient of expansion. The slightest change in temperature is notable when mercury used in a thermometer. The metal has a shiny appearance and doesn't stick to the glass surface of glass. Also, mercury has a high boiling point which makes it very suitable to measure higher temperatures.

(Source: http://www.mercury-thermometer.com http://www.surgicalshop.com/health-monitors-diagnostics/mercury-thermometers-clinical/index.php )