New mentality: take notes when you're supposed to and do what you're supposed to do.
STAT EDIT L1 is x and L2 is Y STAT CALC 4 ENTER for slope= 0 if 0/n
undefined line: vertical and looks like n/0
STAT EDIT 5 if you lose where you're @ w/0 calc. make this chart and use any #'s for x and graph yourself