Google Charts API use

Hello, I'm testing Google Charts API plugin for rails and have a few questions about it's use (I searched for a developper documentation for about an hour without founding anything really interesting):

Here is my test code: # Testing google charts api chart = GoogleChart.new chart.type = :bar_vertical_stacked chart.height = 400 chart.width = 600 chart.data = [@totalAmount, @totalPercent] chart.colors = '346090' chart.labels = ["total", "percent"] @small_sales_chart_url = chart.to_url

And in the view: <%= image_tag @small_sales_chart_url %>

The generated graph url is: http://chart.apis.google.com/chart?chs=600x400&amp;cht=bvs&amp;chco=346090&amp;chl=total|percent&amp;amp;chd=t:300\.0,100\.0

This is great, but I would like to know how to:   - Set the space between each bar   - Define the y axis labels   - Create a bar with values that can be negative   - Write the value of each bar directly on the graph ....and so many more.

If anyone knows where I could find a complete developper guide that would be great, if not maybe you can help me with those few questions in the meantime.

Thanks!