I have several Excel xy charts plotting data that updates
automatically.

The x range varies from 0 to 40, 40 to 80, ... up to 560 to 600.

I want the chart x values to start at the lowest x value in the data,
but it actually starts at 0 for all values up to 160, then does what I
want for higher x starting values.

I have the x axis auto button selected.

Can anyone tell me how to stop the minimum value defaulting to zero?
Excel 2003 and Windows XP.