It's normally a figure based on the twin engine HOGE weight for take off from an offshore deck. HOGE is based on twin engine max continuous power and if you were e.g. pulling 100% OGE you would have no more left for vertical performance. If the hand of God sent a little puff of downward moving air or you attempted to move forward you would descend. So take the weight for your OGE figure at the appropriate OAT and height (=100% thrust) from the RFM HOGE graph. If this were e.g. 10,000 units, then 10,000 x 100/105 would give you a new weight of 9524 units. If you were hovering at this weight you would have a 5% thrust margin in reserve for your vertical performance.