Let me elaborate a little on this topic.  It is something that confused the hell out of me when I first started using Expedition.  

Firstly the Open and Save buttons/menu options in StripChart only refer to the StripChart configuration - i.e. what channels you want to view, how many channels to display, etc.  Define a set of information you want to analyse and save that configuration so you can do a similar analysis in the future.  I have 3 or 4 StripChart configs that I use for different purposes.

So lets say you have been sailing all day and in the evening you want to review your racing.  Expedition has saved all appropriate channels in the log file  (Expedition\Log0\YYYYMonth_XX_n.csv)

Launch StripChart and choose whichever StripChart config you want to work with (via drop down list or via Open - or define a whole new one).  Now under the file menu select Load Log File.  Browse to the log file from today's date.  Also load in an appropriate polar file if you are interested in looking at Polar% etc.

Now you should see your day's sailing in StripChart format.  You can analyse specific legs/tacks by using the wand functions - set a beginning and end wand point, Stripchart will show you the average values and deviation for each channel.

If you have some interesting data, you may want to save it as a test.  Interestingly this results in the data being written back into the Expedition database.  Pick nice clean sections of your stripcharts, between tacks/gybes, click on Save Test button.  You can add a lot more info about sea conditions, helmsman, trimmers, sails etc.  This all gets saved off for analysis later.  You can use it to analyse and edit your polars.

You can also do a quick comparison of two racing legs within StripChart.  Under View set the number of wands to 4.  Then click the beginning and ends of two separate legs/tacks.  It will immediately show the average for each channel during each period.

Hope that helps.

let's have an amen to that! Thank you Fergal, that was excellent.