As a safety precaution, please unplug your battery, audio cables, and headphones for now.

In this next section you'll be plugging your battery back in, but for safety reasons please be sure you don't have anything plugged into either audio jack.

Here's a note on safety with powering potentiometers, which I added after a student and I witnessed a plume of smoke rise from their potentiometer:

(At around 1:04 I say multimeter when I mean potentiometer. Don't worry, unless your multimeter gets hit by lightning, it will never start smoking!)

And now that that's out of the way, back to our previously scheduled measurements and calculations:

In this next section you'll be reconnecting your audio input and output. For safety reasons please be sure to disconnect your battery.

Also make note that you'll have to test audio on a powered speaker, not headphones. In the next section on parallel we'll get into why you can't use headphones.