In article , Adm wrote:
[...]
Any value of the output signal above dark current level corresponding to
this
part of the chart is deemed not to have come from the chart at all but
from
light scattered in the lens, and the circuitry is adjusted accordingly.

Ah - so that's where my licence fee goes......

Yes, it goes into maintaining broadcast picture and sound quality in various
ways that most people probably don't even know about. It also goes into
training people to be able to do this, and these people gradually migrate
into the ITV and freelance market, where there are hardly any training
courses except manufacturers' proprietary ones on specific items of equipment
unless individuals are prepared to pay for them at costs in the region of
1000ukp per week. Thus, a great deal of the expertise in daily use in
broadcasting *everywhere* in the UK is provided through the BBC.

Rod.