Thermometers are often placed everywhere around houses and most cars even report the outside temperature now too. However they can fluctuation greatly. For instance, a parked car is likely to read much higher than a moving car, while the wall of a house could be radiating heat (particularly at night) which will artificially inflate the temperature.
This doesn’t mean the temperature isn’t real, the physical temperature is the temperature displayed on the thermometer – but it can’t be compared with another temperature elsewhere. For instance, we can’t say that because the car says it’s 40C in Sydney, but some one’s verandah in Alice Springs says it’s 38C that it’s hotter in Sydney because they’re measured differently.
Measuring temperatures by Stevenson Screen ensures consistent results – which is crucial for record keeping and statistics. So if you’ve ever wondered why your temperature differed to the official temperatures listed by the Bureau of Meteorology you now understand why!