In article <3258B30F.5A63@iac.co.jp>, silence@iac.co.jp says...
[much deleted about set-up for comparison of meters - well done]

>Pentax digital SpotMeter read 10
>Both Nikon read 9
>Gossen read 9 1/3
>
>(values are given in EV. Values converted from Nikon reading to EV with
>Pentax chart on the dial).

I am not surprised by the above (did you meter at the same angle to the
grey card with each meter, without moving the grey card? Though the sky
was overcast, did you re-meter with each to make sure that the source
light was not changing? You did block the eyepieces of the SLR's while
metering? You also made sure that the metered area covered no more than
the card with any meter?) - older Nikons typically either read correctly,
or overexposed 1/3rd stop, though Nikon AF bodies seem to be calibrated
within 1/6th stop of what I consider correct. My guess is that following
either the Gossen or N90 meter would produce fairly well exposed slides,
but that the Pentax would not. Try shooting any 100 speed slide film,
using each of the three meters under a variety of lighting conditions
to see which meter is most correct.

>Regarding filters, I own a orange filter and amber filter made by Nikon.
>The reference given by Nikon doesn't match the standard designation
>given by most photographic books, i.e. Kodak chart:
>- The L1BC is apparently an UV or Skylight filter

Multicoated skylight.

>- What about A2 and A12 (A for amber). Do they correspond to 81A and
>81B?

They are for slight warming, and for correcting tungten type film
for daylight use.

>- What are these B2, B8 and B12 (B for blue)?

They run from slight cooling for early or late day shooting with slide
film to full tungsten color correction.

>- What means the S after the ND filters (some have it like ND2S, some
>don't like ND4)?

Dunno...., sorry!

>- Is ND2 exp. correction 1/3 or 1 f/stop? What about ND4 and ND8? (I
>don't own this filters so I can not find out myself)

1, 2, and 3-stop reduction.

>- Should I buy Nikon filters or is there a better brand out there?

Nikkor filters are about the best you can get, both optically and
in physical design and construction (glass is not held rigidly in
the rigid, thin metal rim).

>Thanx in advance for your help
>LdS

You're welcome!
Hope This Helps