"TonyL" wrote in message
...
Dave Plowman (News) wrote:

You do need to use a reasonably accurate combination of level and time
though - like any exposure. And the coated board is rather expensive
to experiment with.


I would guess for calibration....a timer and a 1 cm by 10 cm strip of
coated board with sections exposed for various time periods.


Not a lot of use with sunshine, as the UV content varies from
minute-to-minute depending on cloud cover.

David.