Marl at Doubling Stocks just picks up Penny Stocks from a list. The price per share of this stock is also very less (in between 0.10 to 10$ etc). In general such stocks are highly volatile and they always trades with high volume so it's obvious that this types of stocks can show a 100% to 200% change at either direction per day.

One can easily earn 400% of initial investment using Stock Trading Software (Marl) at Doubling Stocks. 

In fact I have been trading from past 2 years and I myself have good experience in Stock Trading. But there too many companies listed on stock exchange so it is impossible to hunt such stocks from that big list, as this types of stocks are mostly unknown. I also found that instead of investing into big and famous companies stock like Coca Cola, investment in unknown and small cap stocks at the particular time when price is around bottom then return is always good.