If anybody has a project on which they have to calculate the critical path, you can give my critical path calculator a spin:
http://sporkforge.com:424/sched/critical_path.php
It's quick & easy (and free 8)). Check out the sample project (button on the right) for a demonstration.
Web-based Critical Path Calculator
i checked out your tool and it's not that accurate, i end up doing the calculations manually
Web-based Critical Path Calculator
here is another list of tools....
http://critical-path-calculator.qarchive.org/
for your calculator.. :)