UIPickerView in iphone's clock timer app

I'm creating an app开发者_C百科 that take input from the user in the form of minutes and seconds, just like the apple's clock timer app. In the two components of the UIPickerView in apple's app, you can scroll the duration but the word "hours" and "minutes" stay in the one place, they don't scroll with the numbers even though they are in the same componant. Does anyone know how this is done?

Thanks in advance

Is it overlayed on top of that view, with some transparency?