Even simpler, forget a custom App, depending on the kind of data you're using a properly formatted printf(), Hyperterm and Excel are your best friend.
I had to monitor the PID response for last years robot and a bunch of numbers wasn't doing it for me, so I had a printf like this:
Code:
printf("%d,%d,%d,%d,%d",kp, ki, kd, error, output); // This is a loose guess at what it was
Then I told HyperTerm to save to a file, and let the robot run, then using Notepad++ (it handles large text files better than notepad does) I trimmed out the section I needed and imported to Excel as a CSV (Comma Separated Values) file. Then I re-saved to .xls and started graphing, thanks to Mark McLeod for that awesome tip.