My instrustor who is away for a week left me a sheet titled "Patterns With Quarter Notes For Developing Left Hand Positions On Each String". I've been practicing notes on the E String but came across a symbol that resembles a box with lines protruding from the top left and bottom right sides. I think it's called a "Natural" but have no idea how to play the note. For example, there is an F Sharpe followed by another F with what I think is a natural symbol in front of it. How is the 2nd F played on the E String? I've tried to find the symbol in my Bass Guitar For Dummies book but I couldn't find it. Any help appreciated. Tks!