In the last two decades, there has been a significant change in the technology of clinical thermometry. Mercury-in-glass thermometers have been replaced with electronic devices that offer faster readings with minimal inconvenience to the patient. Each user should be aware of the characteristics and limitations of these devices to interpret correctly the temperature reading on the display. The article provides an insight into commonly used clinical thermometers, how they determine each temperature reading and, crucially, how users affect the measurement process.