Grid lines for calendar year data sets

[die...@gmail.com]

Does anyone know how to change the grid lines for time based data such as US unemployment rate? 

http://www.google.com/publicdata/explore?ds=z1ebjpgk2654c1_&ctype=l&strail=false&bcs=d&nselm=h&met_y=unemployment_rate&fdim_y=seasonality:S&scale_y=lin&ind_y=false&rdim=country&idim=country:US&ifdim=country&tstart=1015660800000&tend=1347174000000&hl=en&dl=en&ind=false&icfg

The grid lines are not January to January and the resulting visualization can be confusing unless you pay close attention.