Repeat exactly?

In a recent Interview on the Harvard Business Review Podcast Daniel Pink (http://www.danpink.com/) stated that repeating a customer's order exactly back resulted in %70 higher tips. I'm not sure where the numbers came from or what this is based on but it can't hurt. Repeating back exactly does show that you are focused on the customer and are taking the time to get the order exactly right. I can see where this could help.

However, 70% to me means that where you would normally get a $10 tip you get $17 instead? It still seems a little high to me.

If you are tracking tips, try this and please tell me what happens. I'd expect a much smaller increase but I love it when I'm surprised.