I have four I use regularly, plus my kids are in junior tennis and they each have a racquet. I know nothing about stringing. What is a good machine to get and can you teach yourself or do you need someone to show you? I know I probably want at least the machine with the crank as opposed to the drop weight because I know with the drop weight I will have trouble figuring out how much slack to put out there to get it level. Any ideas? Thanks!