I have data for a line chart values that rise and fall over a given length of time.  It produces something equivalent to a sine wave.  The x-axis are hour increments.  I would like to put a minor grid line (or major) at the end of each day.  That is easy if I have say 72 hours worth of data.  I just set AutoRange = false, Minimum = 1, Maximum = 72, and Unit 24.  The problem comes in when my data series does not start at the beginning of the day.

For instance, if my series starts at say 6:00 am, then I would want to put the first minor grid line at the end of that first day which would be at unit 18 and then from then on every 24 hours (units).

Unfortunately, I have not figured out how to do this if it is possible.  If there was some kind of starting offset as to where the range value starts for the first data point so that the grid starts counting the range at that point and then when it hits my unit value, it would put the minor grid line.

Any thoughts as to whether or not this can be accomplished?