OK but ... let's say you have to have around 10THash at this point which generates ~31$/week ... you invest back 30$ and earn 1$ ... that means you end up with additional 0.2THash and 1$ earnings per week ... for 10THash the ROI at that rate is around 25 years or 1400 weeks ...
Buying 0.2THash weekly you get 2% increase in your mining power (when starting at 10TH) but you further your ROI by ~30 weeks (as you earn 1$ + 2% per week) ...
Or maybe my math is messed up ? ;D
does not matter what the math says because I'm investing bitcoin paid to me by my contract to increase my daily payments and maintain the longevity of my lifetime contract, the profit comes from bitcoin price going up and me having more valueable btc on hand and being paid daily, than it cost me to upgrade every week