On Tue, 29 Dec 2009 21:33:28 -0000, Martin Rowley wrote:

.... the Internet is awash with these calculators: the problem is
knowing which ones are right!

This one *appears* to do a good job, but I haven't checked it across a
broad range of readings ....

http://www.srh.noaa.gov/epz/?n=wxcalc_dewpoint

I can't get that to work, keeps asking me to enter the dewpoint temp
and units (which is a radio button with one enabled anyway). Isn't it
supposed to be working out the dewpoint given the pressure,
temperature, wet bulb and RH?

Yersterday I found:

http://www.decatur.de/javascript/dew/index.html

Feed it temperature and RH and it returns dew point, probably not
100% accurate but close enough? The "about" page explains it. Not
that I understand any of it but it looks convincing. B-)

--
Cheers Dave.
Nr Garrigill, Cumbria. 421m ASL.