what happen if I directly assign the uncertanty to the capacital cost as +50/-30 as AACE standard. What this potential fluctuation will cause.

update: something like there is a 50 to -30% UncertaintyAACE standard) on my capital cost, so my break event prise also have some change. so is there any risk behind this? and describing that50 to -30%AACE standard) are the reasonable limits of capital cost