How would I get a cron job to run every 30 minutes?

Question

I\'m looking to add a crontab entry to execute a script every 30 minutes, on the hour and 30 minutes past the hour or something close. I have the following, but

Answer 1

You mention you are using OS X- I have used cronnix in the past. It's not as geeky as editing it yourself, but it helped me learn what the columns are in a jiffy. Just a thought.