Digital thermometers work quickly and are easy to read, but are they as accurate as conventional thermometers?

Researchers at Massey University recently set out to find out. They compared four different brands of digital thermometers with two brands of mercury thermometers and one containing ethanol. For the first part of the study, each thermometer was submerged in water of a consistent temperature four times and the average readings were documented.

The researchers found that five of the thermometers produced readings within .07 degrees Celsius of the reading on the reference thermometer (a mercury thermometer brand most often used by the clinic), but two of the digital units registered lower average temperatures. One produced a reading lower by .2 degrees and the other by .1 degrees.

The thermometers were then tested on cattle, horses and sheep. The readings were used to determine that the study horses had an average temperature of 37.4 Celsius (99.32 degrees Fahrenheit). The researchers found, however, that on average two digital thermometers registered lower temperatures and the alcohol-based thermometer recorded a higher temperature. Overall, the temperatures recorded ranged from 36.3 to 38.9 Celsius (97.34 to 102.02 degrees Fahrenheit). The researchers noted that the digital thermometer that produced the fastest results had readings that varied the farthest from the average.

The researchers speculate that the size and shape of digital thermometers may affect contact with the rectal wall and thus temperature monitoring. Noting that inaccurately low readings could prevent detection of a fever in a sick horse, they call for monitoring the accuracy of digital thermometers as that technology becomes more popular.

Reference: “An analysis of the effect of thermometer type and make on rectal temperature measurements of cattle, horses and sheep,” New Zealand Veterinary Journal, September 2014

This article first appeared in EQUUS issue #451, April 2015.