The club where I play at hosted a very big squash event and there was this Indian guy there who was stringing his racquet by hand between matches. It was awesome! He plucked each string a few times and listened to the tone. He would close his eyes and listen to the tone then either clamp the string or increase or decrease tension until he reached his desired tension. He won the tournament so he must have been doing something right. He told me that he would hum the tone that he wanted and if it matched then he would clamp it and tension the next string.
-Tennis is an easy game made complicated by idiots-