On Fri, 10 Dec 2010 19:52:55 +0000, Ian Jackson
wrote:

Do a Google on "Grease Spot Photometer" (back to school physics, over 50
years ago!). Very simple to make, and pretty accurate.

Hi Ian,

A very good suggestion which immediately led me to:
http://www.phy6.org/outreach/edu/greaspot.htm

A variation of this that I calibrated in the lab is an Optical
Pyrometer:
http://www.pyrometer.com/Pyro_Optical.html

Comparison measurements can be very accurate iff what you are
comparing to (aka standard) is known to sufficient accuracy. Both
references provide more than enough to inform the reader with the
essential details.

Slightly more elaborate methods of measuring RF power fall into the
Calorimetric method (actual heat). Hewlett Packard made the ultimate
heat transfer standard - the HP 434A power meter DC to 12GHz!

73's
Richard Clark, KB7QHC