Question about "iImmigrationWeight" and "iImmigrationWeightDecay"

UnitTypes CvPlayer::pickBestImmigrant()
{
	std::vector<int> aiWeights(GC.getNumUnitInfos(), 0);
	for (int iUnitClass = 0; iUnitClass < GC.getNumUnitClassInfos(); ++iUnitClass)
	{
		UnitTypes eUnit = (UnitTypes) GC.getCivilizationInfo(getCivilizationType()).getCivilizationUnits(iUnitClass);
		if (NO_UNIT != eUnit)
		{
			int iWeight = GC.getUnitInfo(eUnit).getImmigrationWeight();
			for (int i = 0; i < getUnitClassImmigrated((UnitClassTypes) iUnitClass); ++i)
			{
				iWeight *= std::max(0, 100 - GC.getUnitInfo(eUnit).getImmigrationWeightDecay());
				iWeight /= 100;
			}

			aiWeights[eUnit] += iWeight;
		}
	}

	UnitTypes eBestUnit = (UnitTypes) GC.getGameINLINE().getSorenRand().pickValue(aiWeights, "pick immigrant");
	FAssert(NO_UNIT != eBestUnit);
	if (eBestUnit != NO_UNIT)
	{
		changeUnitClassImmigrated((UnitClassTypes) GC.getUnitInfo(eBestUnit).getUnitClassType(), 1);
	}

	return eBestUnit;
}