In one sentence, describe what the following article is about:

While you're transposing concert pitch music to play on an E-flat instrument, that doesn't necessarily mean that the music itself is in the key of C. When you moved the notes before, you were simply moving them the correct interval, ignoring the key signature. Now you need to move the key signature as well. The key signature is the group of sharps or flats noted on the sheet music next to the treble clef. Each key signature has a different grouping of sharps or flats. The circle of fifths is a tool that allows you to find the right key signature for your transposed music. Using the circle of fifths, you can determine how many sharps and flats are in your new key signature. If you don't already have a copy of the circle of fifths, you can download an image for free online. Simply do a search for "circle of fifths" and pick one that you like.  If you moved the notes up a major sixth, start at the original key and move 9 half-steps clockwise. That is your new key. If you moved the notes down a minor third, start at the original key and move counterclockwise 3 half-steps. That is your new key. Check your new key signature on your circle of fifths to figure out which notes should be sharp or flat. Mark these on your staff paper next to the treble clef.  The circle of fifths will tell you which sharps and flats you need. For example, suppose your concert pitch music was in G. You transposed the music to E flat by moving the notes down a minor third. From the circle of fifths you can see that your new key signature is E major. E major has 4 sharps: F, C, G, and D. To work out which notes should be sharp or flat, you can use a mnemonic device. For sharps (the keys you find moving clockwise), remember the phrase Father Charles Goes Down And Ends Battle. The first letter of each word corresponds to a note. So if E major has 4 sharps, the notes that are sharp are the notes that correspond to the first 4 words in your mnemonic device. For flats (the keys you find moving counterclockwise), you can read the same mnemonic backwards: Battle Ends And Down Goes Charles Father.
Check the key signature of the original music. Use the circle of fifths to find your new key signature. Mark your new key signature on your staff paper.