There's a great book called Practical Astronomy with your Calculator; I wonder what the astrological analog would be.
You run the algorithm using the exact time and place of client's birth. This is, of course, bullshit — some random predictions, which are deliberately written in quite ambiguous, but somewhat flattering style (the genre was perfected in hundreds of years). But now, the most interesting part comes to play.
You tell the client one or two predictions from the list, starting from the most vague and/or flattering (like "you are probably going through worse times than you deserve"), and observe the reaction. If it is positive, you probe the next close thing from the generated set, and so on. If you are good in reading people and adjusting your response according to body language feedback, you can generate the set of predictions or advices so accurate you will impress even yourself, even if you don't believe any of the astrological bullshit. Most astrologers don't.
It's very unlikely astrologers have created or added anything that's useful or applicable to astronomy. It's more likely that they've taking things astronomers have discovered and used and worked that into their quackery to make slicker quackery.
I also think it would be interesting, albeit in a totally different way, to know what "algorithms" they're up to in there, even though it's bullshit.
Definitely agree about their quackery.
It could well be they are doing epicycles caculations to determine stellar positions etc