How to figure out where the UV shows on the Mesh? How to figure out where the UV shows on the Mesh?

I know that there is an option or button to find out what part of the UV mapping matches up with the mesh so that fixing problems is easier. 

Does anyone know what that option is?
That button right there is probably what you want. Also keep in mind that by default, only faces you have selected in edit mode show up in the UV editor.