I am reading the error through the serial port. I moved the application to Visual Basic 6 so I could add time measurements and got an average of 47 milliseconds per reading with a standard deviation of 6 milliseconds. This is about 5 readings per second slower than just in the VBA Excel worksheet, so I am inclined to keep it the worksheet where I can get a solid 25 readings per second. This is not stunning resolution, but I think it is adequate for tuning purposes.
The program reads the returned text string, and parses it into the Excel workbook. Then I use the Hex2DEC worksheet function to convert the output into decimal. I'm most comfortable with graphing in Minitab, but obviously once this data is in Excel you can use Excel's graphing functions to make the same kind of charts.
As for the serial interface, I'm kind of a newbie at that kind of programming. I came across an ActiveX freeware control that is similar to Microsoft's non-free comm control called NetComm. Anyone using my application would have to have to download and install this control here:
http://home.comcast.net/~hardandsoftware/NETCommOCX.htm
I put the Excel workbook application here:
http://www.geocities.com/eba1972/ViperServoAnalyzer.xls