Three examples are worked through:
1. Suppose an observer wants to observe a line at 10 
m of strength 15 Jy
and reach a S/N of 30. Looking at figure 6.2 we see that
it takes 2500 seconds to reach 1 Jy at a S/N of 20. Our line is 15 times
stronger, so it will take 
times less to reach a S/N of 20, but we want
a S/N of 30 requiring 
times more. Doing the calculation we find
it takes 
seconds. This is less than the minimum 273
seconds so it will take 275 seconds. And PGA confirms it will take 275
seconds (to which should be added the 180s slewing time).
2. Suppose an observer wants to observe a line at 25 m of strength 0.5 Jy
and reach a S/N of 30. Looking at figure 6.2 we see that
it takes 2500 seconds to reach 0.8 Jy at a S/N of 20. Our line is half as
strong, so it will take 
times more to reach a S/N of 20, and we want
a S/N of 30 requiring times more. Doing the calculation we find
it takes 
seconds. PGA reports it will take 10500
seconds (to which should be added the 180s slewing time).
3. We want to observe three lines. They are lines of strength 1 Jy at 2.8
m to a S/N of 15, 0.5 Jy at 5 m to a S/N of 10 and 10 Jy at 11
m to a S/N of 100. Doing the calculations we see that the 2.8 m line
will take 275 seconds, the 5 m lines will take 4000 seconds and the 11
m line will require 1900 seconds. The 2.8 m and 12 m lines can
be done simultaneously, so they will require 1900s, to which should be added
the 4000 seconds for the 5 m line. Therefore the observation will take
about 5900s (to which should be added the 180s slewing time). PGA reports it
will take 5800 seconds.