http://btcdou5ipdmzh2qvn76az5pt6j6gn5mhwtfgb2tsa3hscmbqkdetrgqd.onion?i=whydoubling
The only catch is that you need to know when is down to buy, and when is up to sell. But that is simple because we have a smart algorithm that analize the bitcoin blockchain and sees when is down and up, as per this graphic We are investing our bitcoin and double it every 3 days.