Updated first post with findings. Revised formula

Weapon/Amps Efficiency Formula

**Efficiency=(x-2)(23x-42)/2**

x=max_dmg/cost (maximum dpp)

All but verified by MA

Economy enhancer does not adjust efficiency rating

Accuracy enhancer does not adjust efficiency rating

**NOTE:** As the relationship between efficiency and dpp is nonlinear, you will get different results if you try to calculate efficiency from a combined dpp item. Combining efficiencies is calculated on cost (decay+ammo), compared to dpp which is calculated on dmg*eco

An item with max DPP of 2 or lower will have efficiency of 0.

the max attainable economy rating happens at 4.86DPP (Impossible without an items already at 100% efficiency)

**Interesting findings from this**

I suspect the Unique Legend War axe and imp 7 knife have incorrect dpp's in entropedia.

Test: Looked up Mann MPH DLXe in auction, which has a very close dpp in entropedia as ?Unique Legend

From entropedia:

Mann MPH DLXe=2.174

Unique Ax=2.164

The implies efficiency for Mann MPH DLXe should be 0.7% (correct, confirmed in auction)

The implies efficiency for Unique Axe should be 0.6% (incorrect, auction states 0.0%)

Economy enhancer does not adjust efficiency rating

Accuracy enhancer does not adjust efficiency rating

**Conclusion:**

Displaying efficiency is a good thing! This prevents discoverers of unique weapons from lying about economy, as we know the conversion rate.