for mining;  the only thing you can factor in is the payback/ROI total vs. the value of the gear if liquidated for sale.  This is true scaling roi in my eyes.

but I don't count on getting things by a time.  I am just excitedwhenever anything is coming in.  Especially is it has paid itself physically off, and/or its profitability margin takes theoretical ROI sooner then the 6-3 month mark.