Derived from equations 7.3.1 and
12.2.2, the total number of old civilizations
in the galaxy is the sum of all spectral classes:

N_{OldZivGal}
= ∑ N_{zx}
= A·∑ (F_{x}
· F_{ph}
· F_{k }·
F_{Liz}·
F_{u}) 


7.3.4.1
Equation 

Then the equation can be written like this:
7.3.4.2 Equation 

This results in the number of old civilizations
in the galaxy:
7.3.4.3 Equation 

According to equation 6.2.4, the following probability
for a civilization level can be established :
The total probability results from the sum of the
individual probabilities when a set of civilization
levels is considered.
Old civilizations emerge only from level 8.
Hence the probability of an old civilization:
F_{z} = 14.400/7.301 · 1:64
F_{z}= 0,030817 ¤ 1:32
F_{z}= 1:32
So for the number of old civilizations in the galaxy:
7.3.4.4 Equation 

Adapted to the model used so far:
