Can some one explain how the world default settings work
What about them would you like to learn? Most of them pretty much explain themselvs.
the how scaling works exsactlly
So here’s my understanding of it, I might be totally wrong.
Monster scaling is a factor that affects how fast zombies become stronger; over time, you’ll find that you’ll see fewer and fewer standard zombies and more corrosives, brutes, hulks and so on as your world becomes older.
The scaling factor option affects how fast zombies upgrade: a factor of .5 makes them upgrade faster, a factor of 2.0 makes them upgrade slower, and a factor of 0 disables scaling entirely.
Pretty much, though IIRC there might be some differences in exactly how that works between the experimental and .C, so if you aren’t using the experimental you might want to read the explanation closely to see how exactly it is working.
I curious on item scaling
Set Item Scaling to 2.00 and you will get 2X as many items spawning around the world.
This. The tooltips pretty much explain the rest. It just scales from there.
I set my zombie scaling to 28.0, and I saw 3 hulks in the first day in the starting city. That same happened with value 0.10, too.
Static spawns, spawn rate 2.5
Version 0.C-3467
Explain that. 
Edit 1:
From the savegame folder, worldoptions.txt
[QUOTE]
#A scaling factor that determines average time in days between monster upgrades. Set to 0.00 to turn off monster upgrades.
#Default: 1,00 - Min: 0,00, Max: 100,00
MONSTER_UPGRADE_FACTOR 28.00
[/QUOTE]
I assumed that based on that description and the “28”, monsters would upgrade every 28 days on average. Is this a false assumption? Or did I make them upgrade 28 TIMES FASTER than normal?!
Edit 2:
…I didn’t think that one through, did I?
I mean, at value 1.00, they would upgrade once per day, is that so?
That would mean at 28.00, they would upgrade… in 1/28th of that time? Or once every 28 days?
Why can’t you make descriptions that can’t be interpreted in multiple ways? 
Basically what I want is super slow evolution. But I’m still confused if I need a value of 0.01 or 100.
some high level zombies spawn on day one. even with scaling off. if i remember the post right the scale is how many seasons it takes for half the normal zombies to upgrade.
Oh wow, I did that backwards last world. I’m amazed I lived as long as I did.
It’s one of the things that got “flipped” in various experimentals in order to make it make a bit more sense. If you were using an older version then it worked the reverse of the way it does currently.