Hello Darren Yes and one of the problems you can have is that the screen can actually create its own micro climate it may be stated that the larger the bulk of a screen, the stronger the microclimate within the screen and the more the sensed temperature deviates from the real air temperature any design of a thermometer screen is a result of compromises. Hense calibration Finding the optimal design is a serious challenge I dont think folk realise what goes into these things.
Funnily enough I had a quick look earlier at the Davis range of weather stations on a certain online shop - I know they're good quality, but I was surprised to see that they apparently don't need to be in a Stevenson screen (so presumably the Met Office-approved instruments are something else - wonder what brand they use?)
Then you get fan-aspirated options, daytime only or 24-hour and yes - calibration rears its head. The shop says, and I quote:
"Recalibrating the temperature humidity sensor in the field requires a visit to site from someone with a certified accurate sensor. This would need to be a reference instrument with an annual certificate from a UKAS test house. If you need to do this then we consider that it is actually more cost-effective to replace the temperature humidity sensor with a fresh one."
This will, doubtless, be what's happening at Cambridge as we speak (well, maybe on Monday!)
If a national record is to fall everything has to be absolutely 100% certain. Brogdale passed the checks in 2003, it remains to be seen whether Cambridge does as well.