I'm working through Berklee Press' Modern Method for Guitar 1. I start every new piece at 40 1/8th notes per minute, so 20 bpm. 40 bpm (1/4 notes per minute) is the lowest my metronome goes, so I just make each tick an 1/8th note instead of a 1/4 note. 40 bpm seems like it's too fast for me to read a new piece.
For most pieces, I just start at 20 bpm and I work up to only 40 bpm. I realize that that's still very slow, but I'm not trying to memorize the song, nor prepare for a performance. Working up to faster speeds seems like it's less about reading music and more about muscle memory. For the pieces or exercises that are more speed specific, I will work up to 80+ bpm.
The problem that I'm wondering about is that I'm not really getting faster at sight reading music. Every new piece I start at 20 bpm. I can't imagine sight reading a song at its intended tempo.
Is there a better way to approach this. Instead of starting slow, should I start faster and just make a ridiculous amount of mistakes? I already make mistakes at 20 bpm. I have seen questions and answers like this one that say to slow down to practice songs. Should I burn my guitar and cut off my hands?
I realize that each piece is getting more difficult, so maybe if I were to start at the beginning of the book, or find another book with easier pieces, then I could start faster. I would appreciate your thoughts on this!