Unit 3 - Tuning a Pure 4:2 - Example

The procedure is simple:
1) Tune A4 as a clean trichord at 440 Hz +/- 1 cent
2) Mute one string of F3. Clean up the DSU.
3) Mute one string of A3. Clean up the DSU.
4) Play F3-A3 and F3-A4. Listen at A5. Compare beat speeds.
If F3-A3 < F3-A4, raise A3
If F3-A3 > F3-A4, lower A3
F3-A3 = F3-A4, you've got a pure 4:2.
Remove the mute on A3 and tune it pure to the other two.

The following video explains the theory of the 4:2.

Rewatch theory lessons 6, 7, 8, and 9 if you still do not know how to do this!