Sets how large the labels are rendered. You can use positive numbers 2, 3, 4, etc for point sizes, or negative numbers for Angstrom-based sizes. Default is 14 points. Labels in Angstrom-size scale with the distance from the front plane, labels in point-size don't.
# set the label size to 10pt set label_size, 10 # set the label size to 1.5 Ang. set label_size, -1.5 # set label sizes to 1.5 Angstroms -- large!