Whats the switch in my 5th gen prelude for ??

theres a little swith to the left of the radio in my car and i never found out what it is or does , does anyone know ? i didnt see it in the manual =/ .. its just a switch tht goes up an down i thinkits got a red dot i forget its really close to the radio but nothing to dowith the radio im sure ... its on a seperate panel .. just beside the radio to the left .. thanx hopefully its usefull