You press it. The sound changes. You press it again. It changes again. You are confused.
Here’s a concise review of the (presumably for a car audio graphic equalizer/amplifier unit, likely from the 1990s or early 2000s, such as the Pioneer DEQ-7600 or similar EQ models with 45 watts x 4 channels). pioneer eeq 45wx4 instruction manual
You plug the stereo in. The radio works, but the bass sounds muddy and the treble is harsh. You look at the faceplate. You see a button labeled . You press it
Here are some frequently asked questions about the Pioneer EEQ 45WX4: pioneer eeq 45wx4 instruction manual