There appears to be a bug (or an unintended side-effect, anyway) of
adding chbh=a to a bar chart.
Here's the original chart (taken from the API docs, with "chxr"
changed for the Y scale:
http://chart.apis.google.com/chart?chxt=x,y,r&chxr=0,100,500|1,0,227|2,1000,0&cht=bvs&chd=s:c9uDc&chco=76A4FB&chls=2.0&chs=200x125
Important to note, the Y axis has a scale of "0" to "227", and the
chco values are scaled appropriately to match this range.
If I add "chbh=a" to the chart:
http://chart.apis.google.com/chart?chxt=x,y,r&chxr=0,100,500|1,0,227|2,1000,0&cht=bvs&chd=s:c9uDc&chco=76A4FB&chls=2.0&chs=200x125&chbh=a
the Y Axis scale is changed from 0-227 to 0-200, but the vertical size
of the bars is not. The height of the bars no longer matches the Y
scale (in my real world case, bar heights are a % of 227, which works
great if the Y scale goes up to 227).
The same problem occurs if you use "chbh=r,<n>,<m>":
http://chart.apis.google.com/chart?chxt=x,y,r&chxr=0,100,500|1,0,227|2,1000,0&cht=bvs&chd=s:c9uDc&chco=76A4FB&chls=2.0&chs=200x125&chbh=r,1,2