First off, the wiki info for skill weight is wrong to include base skill points into the calculations.

i.e., we'll take a Dark Elf Priest skill leveling as shown below.

Weights:00 00 00 00 02 00 00 00 00 00 02 03 00 02 00 00 03 01: Weights total: 13

Level 1: 15 15 15 15 15 15 20 15 15 20 20 15 20 15 25 20 15 15 : Diff: 0
Level 2: 15 15 15 15 16 15 20 15 15 20 21 17 20 16 25 20 17 16 : Diff: 8
Level 3: 15 15 15 15 17 15 20 15 15 20 22 19 20 18 25 20 19 16 : Diff: 8
Level 4: 15 15 15 15 19 15 20 15 15 20 24 20 20 19 25 20 20 17 : Diff: 8

Without the base 15 skill points, the character levels at 8 skill points per level which is correct and all is well until something hit the 100s.

Level 46: 15 15 15 15 70 15 20 15 15 20 75 98 20 71 25 20 98 43 : Diff: ~
Level 47: 15 15 15 15 71 15 20 15 15 20 77 100 20 72 25 20 100 43 : Diff: 8
Level 48: 15 15 15 15 73 15 20 15 15 20 78 100 20 73 25 20 100 44 : Diff: 5
Level 49: 15 15 15 15 75 15 20 15 15 20 80 100 20 75 25 20 100 45 : Diff: 7
Level 50: 15 15 15 15 77 15 20 15 15 20 82 100 20 77 25 20 100 46 : Diff: 7
Level 51: 15 15 15 15 77 15 20 15 15 20 82 100 20 77 25 20 100 46 : Diff: 0
Level 52: 15 15 15 15 80 15 20 15 15 20 85 100 20 80 25 20 100 48 : Diff: 11
Level 53: 15 15 15 15 83 15 20 15 15 20 88 100 20 83 25 20 100 50 : Diff: 11
Level 54: 15 15 15 15 83 15 20 15 15 20 88 100 20 83 25 20 100 50 : Diff: 0
Level 55: 15 15 15 15 87 15 20 15 15 20 92 100 20 87 25 20 100 53 : Diff: 15

It looks like skill point distribution went and took a vacation after level 47, or when a skill hit 100.

The reason for this is I am writing a tool: http://skyrim.nexusmods.com/downloads/file.php?id=4554

I have worked out the the formula for the first part, but what is going on after level 47?

Hi, Foretrenty. i used your Editor making parts of my own mod. Thanks!

Where did you see that about skill weighting in the wiki? I haven't be able to find it and the tute on making followers suggests that simply using "PC Level Mult" will cause NPCs to automatically increase skill and base stats when it won't. As far as I can tell, "PC Level Mult" only causes automatic leveling and does not affect skill leveling. Skyrim.esm in TESVsnip is showing me ACBS flag data that I don't think is exposed in the CK. I'm beginning to wonder if the skill leveling isn't handled completely outside the NPC data in a formlist or something.

PS: Maybe what you're seeing is why vanilla NPC followers are only set up with a max level of 50 (or less).

the average diff of those 9 levels is about 7...thats close enough for good maths right?

It looks like whatever level up function gets used on the skill weights just gets screwy after a skill gets maxed

edit: we could also call it a feature...its a high level diminishing returns feature for npc level ups! (assuming that the average remains under 8/continues to decrease)

Wiki for skill weights is http://www.creationkit.com/Class.

It looks like everything is random after skill hits 100, but theres got to be a formula there because is it matched precisely in game. I got close several times but I think I might have spent too much time (days) working out formulas to make it exactly as is. I just wanted to finished up other parts of the tool and release the new version.

In regards to ACBS I think I managed to get most of it, if not all. I'll update the UESP soon as I hit the next milestone. Skill leveling is according to class. And Attributes and Skill base are recorded in Race.