I think this is great! A bitcoin calculator that factors in lead time is absolutely necessary given the current state of mining and preorders. I just have 1 or 2 comments. First, the difficulty increase. I assume that is valued as a percentage but perhaps it could be specified i.e. "Difficulty increase per 2 weeks(%)" or "Percent increase in difficulty per 2 weeks". Also, it states Total Revenue at the bottom but there is no input for mining time frame. I am assuming it is either for a 1 year mining time or it uses the weeks of profitability value to determine revenue/roi. Either way how this is calculated should be indicated or at least let us specify a time frame i.e. revenue/roi for 1 year of mining. Anyway thanks for this valuable tool!