I have a spreadsheet with multiple tabs for entering daily data - to populate
a chart on each tab. The spreadsheet data is backed up & then wiped out
monthly.

The chart keeps a daily information, as well as lines for 2 & 3 sigma limits
based on the previous month's data.

The Y-axis varies on each tab - depending on the difference between the
upper & lower sigma lines.

Since the sigma ranges change monthly, it doesn't work to just put in a set
y-axis min & max.

With auto-scale on, sometimes Excel re-scales after entering the daily
information, other times it doesn't (it sets the automatic minimum to zero,
when it should be around 400 or 600).

Is there a way to force Excel to rescale & not see zero?