On 23 Sep, 17:35, Paul Hyett wrote:
How come, when temperature can be measured to an accuracy of 0.1C on
instruments costing under £100, almost all RH instruments quote an
accuracy of +/- 5% at best?

Hi Paul

At Bablake, we have a brand new Met Office AWS, we have a Campbell
Scientific AWS still maintained to Met Office standards and a
conventional Met Office screen with calibrated, Met Office checked
sheathed wet & dry bulbs from which we work out RH each day.

The AWSs have RH electronic sensors, but they don't always agree with
each other, and they can both be several % points at variance with the
wet'dry bulb thermometers. So there you have it - 3 readings every day
and all can be different even in their screens!

However, I don't use a whirling psychrometer very often, but if I did
I thinkk that might be a fourth different reading!

Does that help?

Thought not:-)

Steve Jackson FRMetS
Bablake Weather Station
Coventry UK
www.bablakeweather.co.uk