The idea is simple: enter lines of text and regular expression to check. This calculator checks each lilne against regular expression. If it is matched, line with its line number goes to "Matches" table and counter of matched lines is incremented. If it is not matched, line with its line number goes to "Mismatches" table and counter of mismatched lines is incremented.
Thus you can filter big chucks of text, like log files, with regular expression. Inspired by work, I hope it could be useful for somebody else as well.