Being able to take an accurate temperature is an essential parenting skill, a crucial step in evaluating your child's illness. The glass rectal thermometer is the cheapest way to determine temperature in infants and children and one of the most accurate. Rectal themometers are precise because they pick up heat from the body's core. On the minus side, they're awkward to use with a squirming child, and children generally find the whole ordeal rather difficult. You have to hold the thermometer in place for three to five minutes, and the small black or colored lines may be a bit hard to read until you get the hang of it.
Digital thermometers are as accurate as glass ones, and are faster.
They beep when they're done and are easy to read, and the pacifier version is a plus with small infants. On the downside, they become less accurate if dropped, and the batteries can expire at a crucial time. Ear canal thermometers are the fastest, least obtrusive, and easiest to use once you get the hang of them. You can get a reading in two seconds. You must learn to tug correctly on the child's ear to straighten out the ear canal.