Changes

Tapping is also an excellent way to perform a trill if you want to change the notes of the trill, say each beat. See the two examples below

Here the tapped note is constant while the lower note moves upwards. We can put our left hand in 5th position and use the index, middle, and pinky fingers to hold the 5, 6, and 8 frets. For beat 4, we simply slide up with our pinky held on the fret, sliding from fret 8 to 10 and continuing the trill.

Here the low note is held constant while the tapped note ascends. We just move our right hand up the fretboard each beat.

Here's a series of trills where both notes change each beat. The low and high notes seem to converge.