Dual six-segment metering

[Artur Ledóchowski]

Hi,
I'm not sure if this was talked through - if so, please excuse me...
I have two questions on the subject:
- is it true that every Pentax camera, that is equiped with a 6-segment
metering, has actually two 6-segment matrixes, or is it only the 645N/NII
that has it?
- what is exactly all about this "dual six-segment metering"? How does it
work? Is it something of a kind of "3D" metering? etc etc...
TIA
Artur