[tekhen]

Mary,

I am sorry I did not make it clear.
There are no buttons.

When you change the volume, there are indication bars on the screen.
When you are in NAV mode, you will see the word volume and increasing or decreasing bars(while changing the volume). The radio's volume on the screen is white and the NAV's volume is blue.

You can easily change both without knowing while the NAV is directing you.

While the NAV is talking you can change it's volume to the desire level.