Both mercury and digital thermometers are about 98% accurate. The main difference between the two types is that most people fidn the new digital thermometers easy to use. Primarily this is because the digital thermometer bleeps when it has found the 'maximum' temperature reading and the result is then displayed on a liquid display screen.
The mercury thermometer has to be inserted for about three minutes before an accurate reading can be taken and sometimes it is hard to read the result ie there is always a fear that it will be one or two degrees 'out'.
So for those reasons it is probably best to use a digital thermometer.
Strip thermometers are also available. These are placed on the forehead and they use heat sensitive chemicals to change colour according to the temperature. However, these only last for a year and may be slightly affected by factors such as the room temperature etc.
The mercury thermometer has to be inserted for about three minutes before an accurate reading can be taken and sometimes it is hard to read the result ie there is always a fear that it will be one or two degrees 'out'.
So for those reasons it is probably best to use a digital thermometer.
Strip thermometers are also available. These are placed on the forehead and they use heat sensitive chemicals to change colour according to the temperature. However, these only last for a year and may be slightly affected by factors such as the room temperature etc.