There is another possibility which sometimes works: by thinking in a different clef. For example, someone who is used to reading music in the alto clef, such as a violist, can transpose up a tone from music written in the treble clef by imagining it was written in the alto clef and playing an octave lower (a note on the middle line in the treble clef is a B, but in the alto clef it is a C). They could also imagine the new key signature of 2 sharps – it becomes a C sharp.