protovis part 2: lines and labels
Getting it lined up
Now we need to line up the rule with the bottom of the chart. Set the bottom to 15, Set left to 24 to describe where the line starts and set right to 6 to describe where it ends. Notice that the lines stick out 2 pixels on either side of the chart.
Next we need to add some tick lines. Tick lines illustrate the scale of the data that the bars represent. Start by adding a comment that notes these are tick lines, then type example.add(pv.Rule).