Secondary Dominants are literally taking your piece in its original Key, and at a point where you are on a note, going to *its* V. You build a new key off of that, assuming it as the *new* tonic. In usage, you don't neccesarily change the key of the piece permanently, but it's a "trick" to build out a climax on a piece.

Rather than your finale having a grand I-IV-V-I sequence to finish it off, you tease the listener by building it as: I - IV - V - V/V (5 *of* 5) - V/IV (5 *of* 4) - V/V - V/III - V - I, etc...

It sounds a little more complex than it *sounds*, but you are used to hearing it as the way 90% of all songs take off into Key changes. If you want the *logical* reasoning for why the V/V and V/IV are so powerful, you'll notice that the V/V is built off of the original vii, and the V/IV *is* the original tonic.

The easiest way to digest it, as well as a huge chunk of the *rest* of music theory, is to memorize the sequence I mentioned earlier (the cycle of fifths), and see how many ways it plugs into theory. Learn it, and the rest becomes a snap. Here is the 30 second primer:

The Sequence: B E A D G C F (it is just a simple sequence, starting at B, all one fifth apart)

The rules that follow this sequence:

1. The order in which flats are added to notation of keys

2. The order in which sharps are added to notation of keys (start at the end and work backwards)

3. A Quick *cheat sheet* to the *most* used chords in any given key (in Western Traditional music, at least). Look at the key you want, your V is one to the right, your IV is one to the left, your Secondary Dominant of V (your *teaser* for a flourished finish) is two to the right.

you'll start to see the pattern for yourself, so I won't belabor the point of it any further.

As to your tuning, a quick lesson in physics, to help you *hear* your tuning a little better, and it works beautifully for violins and Guitars. Listen for the overtones that come out of any particular note when you draw it, especially open strings, as they resonate the best. After the primary pitch, the next set of sounds you hear are the octave of that pitch. The *next* set that you hear are the fifths. If you allow your earing to focus on the overtones, and how well they mesh with the other strings, you will have it tuned damn near as good as an oscillioscope... :)

If you pay particular attention, you might even catch the "Hertz" beats that occur when you end up within 12 Hz of matching a frequency exactly. The closer you are, the slower the *beats* are, until your two waves mesh perfectly, indicating a perfect match. You can experience this phenomenon with the overtones too, but only if you can hear their faint nuances (tune up in a tiled bathroom... :)

Enough math for the day... :)

Domenico