Charts

Is there a good freeware chart software that will import data from Excel?

Or, is there an Excel guru out there who can tell me how to have another axis opposite the y axis so I can plot 2 sets of data against time on the X axis, even though the two sets have different numbers required on their axis.

ie, Time on X

wind direction on Y1 (0-360 degrees on the axis)

Air pollutant on Y2 (0-10 ppb on the axis)

Thanks