IleneK
What do you mean by :"you can zero in on planets in a chart that may be much closer than you thought " ?
In typical modern astrology, position of a planet or point is defined by its longitude, like 25 Taurus. But that is only one point in a two dimensional view of the vault of heavens. The second point of a planet in the heavens is its position by latitude. If I recall correctly, declination is the measurement of a planet's latitude on the ecliptic, between 23º28 N or S (the maximum distance of the Ecliptic above or below the Equator), the Sun's path which the planets follow.
Since the ecliptic is a wide path, two planets could both be at 25 Tau but have different positions on the ecliptic, so not really
really conjunct. It is when they are conjunct both by longitude and by declination that they are really right next to each other and so the aspect is very strong.
I hope this helps. I haven't thought much about declination lately, so I might not be remembering exactly correctly, but this is jist of it.
IleneK
maybe calculatation of the mean distance which includes both declination and longtitude distance ?
I think when you go into averages, you are becoming less precise rather than more. So I suspect the mean distance may not be helpful here, but not sure.
IleneK
and what if the planets are alittle out of orb in both cordinates can
we consider them conjunct anyway ?
You will have to be the judge of how a far is too far out of orb.
When declination added to longitude, it tells you that the closer the two coordinates of each body are to the other, the closer the bodies are in the heavens.