QUOTE(chjj30 @ Nov 13 2018, 23:29)

From here I see it as ADB 18% (22.59 / 25.73) .
QUOTE(iffelse @ Nov 14 2018, 00:17)

Hmm...

Here is my computational process:
Live Percentile Ranges 1.1.0Magnificent Power Helmet of Slaughter--------------------------------------------------------------------
A.
unforgedBase = ( forgedBase - qualityBonus ) / forgeCoeff + qualityBonus
qualityBonus = ((pxp0 - 100) / 25) * baseMultiplier
forgeCoeff = 1 + 0.278875 * ln(0.1 * forgeLevel + 1)
forgedBase = 25.06
pxp0 = 326 (Magnificent of IWmax)
baseMultiplier = 0.0854
forgeLevel = 5
qualityBonus = ((326 - 100) / 25) * 0.0854 = 0.772016
forgeCoeff = 1 + 0.278875 * ln(0.1 * 5 + 1) = 1.1130740820236643420241184075751
unforgedBase = ( 25.06 - 0.772016 ) / 1.1130740820236643420241184075751 + 0.772016
= 22.592651654225599886616291434654
B.
percentile = 100 * (statValue - statMinimum) / (statMaximum - statMinimum)
https://ehwiki.org/wiki/Equipment_Ranges_Heavy#Power_HelmetstatMaximum = 25.73 (Legendary)
statMinimum = 19.87 (Legendary)
statValue = unforgedBase = 22.592651654225599886616291434654
percentile = 100 * (22.592651654225599886616291434654 - 19.87) / (25.73 - 19.87)
=
46.461632324668940044646611512867