[NTG-context] Hobby's Graph package

All, I find myself working my way through John Hobby's "Drawing Graphs with Metapost" again. In Figure 9, the following code has me confused: glabel.lft(image(unfill bbox lab[j]; draw lab[j]), length p[j]); I understand that the glabel command will put the label in this case at the "knot" length p[j]. But when he adds .7, I don't understand why the labels move down. glabel.lft(image(unfill bbox lab[j]; draw lab[j]), 0.7+length p[j]); Can someone help me with this?