.G1
label left "charge"
label bot "pH"
frame solid right invis top invis wid 5.0 ht 3.0
coord x 0, 14
ticks bot out from 0 to 14 by 1
line from 0, 0 to 14, 0
draw of solid
draw af dotted
draw ef dashed
copy "pI.dat" thru X
  next of at $1, $2
  next af at $1, $3
  next ef at $1, $4
X
.G2
