Original post about the Armour Enchancement by u/3235113.

TL;DR: There is a strong correlation between armor points repaired and skill increase, but not without a few contradictions.

Setup

• Lavatory Lv.3, +9.9%
• Hideout management Lv.10
• Light Vests skill Lv.4
• No air filtering unit completed
• All items had maximum maximum durability (e.g. 20/50 PACA armor)

Method

1. Buy an item from the Flea Market within economic reason
2. Write down the current and maximum durability and the repair points to pay
3. Repair item with a repair kit
4. Write down the new durability
5. Write down the new Light Vests skill value
6. Repeat 1-5 for ~60 items
7. Try to apply formulas to find patterns, but find no clear answers
8. Be frustrated and rant on Reddit

Findings

• All skill increases come in intervals of 0.4 (0, 0.4, 0.8, 1.2, etc). Edit: May only be the case for my 60 samples.
  • Reparing a PACA from 0/50 yielded 2 points, while a 13.6/100 Tank helmet yielded 3.6 points.
  • Repairing a 3M armor from 31->38.1 yielded no skill point increase.
• In most cases, durability points repaired has a strong correlation to amount of skill points gained, 20.80 on average.
  • However, there are cases, even within the same item, where this is not true at all. E.g. when repairing a Bomber from 124 -> 145.4 yields 1.2 skill points, where repairing another Bomber from 120 -> 145.1 yields only 0.8 skill points.
• One very weird case where repairing two different 120/150 Bombers to 141.1 and 141.9 respectively both yielded 1.2 skill points, but repairing a third Bomber from 120/150 -> 145.1 yielded only 0.8 points.
• The Bomber beanie and Kolpak Riot Helmet have relatively low repair cost compared to skill increase, but this also depends on the current durability left.
• Repairing the Glorious E and Shattered mask do not seem to increase skill at all.
• Spreadsheet with test data

Speculations

• There is very likely not a single factor deciding how many skill points gained.
• Skill increases could be specific to each item, but that alone doesn't explain the weird Bomber case.
• There could be a random factor involved. The randomness in repairing alone does not account for all of the (weird) results.
• Skill increases may change to become more fluent instead of intervals of 0.4.