"Dave Plowman (News)" wrote in message
...
In article ,
TonyL 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.

Yes - with a light box which I have. But with the sun it would vary
according to time of day and year - even on a cloudless day?

IIRC, some ovens with exposed elements can be used too.

Wouldn't that be IR. ?