Defining a datum for a stacked bar chart

Hi guys!

I'm trying to produce a stacked bar chart which shows the leadtimes between that occur betwee a set of activities. There are 10 activities and they all occur in sequence one after the other. Therefore my stacked bar consists of 10 sections with each representing the number of days between each activity.

There will be several stacked bars on my chart - each represents a particular project and has 10 sections as described above.

When I plot this though, Excel assumes that my datum is zero. This isn't always the case though. For some of the stacked bars the datum will be a negative number (i.e. if the activities started a few days early, and not at day 0). Is there some way that I can make it so my stacked bar starts from an x-axis value that I define?

I've tried to explain this as best I can - if it's not clear please let me know and I'll try and clarify.

Thanks in advance,

Chris