If you've heard about partial capos but don't want to spend a lot on one, you will love this little hack. If you haven't, a partial capo is a capo that only holds down some of the strings (3 in this case), allowing some very cool-sounding chords. This one sounds great on an acoustic, but will probably also be good on an electric.
This is based on these instructions, but as far as I know no one has ever tried this.
So, let's begin.
This is my first Instructable, so if you have any improvements please leave a comment.

Step 1: Materials

You will need:
- Some rubber bands (I used 13, but my guitar has high action.)
- Two quarters
- 2 strips of electrical tape
I also needed another dime, but you may not.

Step 2: Tape the Quarters

1. Stack the quarters on top of each other.
2. Wrap one strip of tape around both quarters.
3. Wrap the other strip perpendicular to the first.
Without this step, the quarters against the strings sound bad and probably aren't great for the strings.

Step 3: Set Up the Capo

1. Flip the guitar upside down
2. Put the pencil underneath the guitar on the second fret (or somewhere else, but this is a good place to start playing with a partial capo).
3. Place a long rubber band on the back of the neck.
4. Wrap another rubber band over the first, around the neck, and over the ends of the pencil.

Step 4: Finish Building

1. Flip the guitar over.
2. Slide the quarter bundle under the pencil, so it covers the A, D, and G strings (or D, G, and B if you want Open A tuning).
3. Add more rubber bands, until all the strings sound clearly.

Step 5: Adjust

If the A string doesn't sound clearly, you may need to slide the rubber bands on the bass side away from the neck.
This worked earlier, but it didn't work for me this time, so I also wedged a dime between the pencil and the quarters so that it presses on the A string and sits over the E string.

Step 6: Play!

Now you're ready to play! This site has some good videos to teach you how. When you need to move or remove the capo, go to the next step.

Step 7: To Move and Remove

To take off the capo:
1. Tie the single rubber band in a knot so it holds the others together. Don't tie it too tight or it will be very hard to untie.
2. Take off the rubber bands from one end of the pencil.
3. Leave the pencil through one loop of the rubber bands.
To put it back on, it's basically the same as making it in the first place, but a bit easier and you don't need to flip the guitar over.