Hello, You really should get rid of the mercury therm. Are you sure it's a mercury therm. and not an alcohol one? Mercury therm. have the silver liquid inside and are no longer sold in any stores in the USA. Alcohol therm. have red liquid in them and are still sold here. Alcohol therm. are still ok to use, but mercury aren't. There was a program where you turn your mercury therm. in and get an alcohol one for free, but I can't remember if it was a government program or a local hospital program or a local pharmacy program. The ear ones aren't as accurate and can be thrown off by too much ear wax build up. They are used in the doctor's offices, because they are more kid friendly. We use a Braun ear therm., which reads exactly the same as our Ped.'s. (We checked it out when our son was sick one time.) The problem we have with our Braun is that we can't store it in a cool/cold room, or it will keep giving us error messages until we have it warmed up. (A real pain in the neck!) We don't use rectal ones, which are the most accurate, because I remember the doctor using one on me when I was around 4 or 5 years old...It wasn't fun, especially since he sterilized it with a lighter. We don't use the mouth one, because our son never sits still. I guess, now I have you really confused. We use the ear one. Our son doesn't get sick enough to warrent a mouth therm.