Precision is a wonderful (and in my opinion, easier than "Standard") bidding system.

All "strong" hands start with 1. A 1 opener shows approximately 16 or 17+ points.

A 1NT opening bid is 14-16 balanced.

All other 1-level openings (1, 1, 1) are natural and limited (11-15).

The beauty of this system is two-fold:

1. You get to start your strong hands at the lowest possible starting point (1).
2. All the other 1-level openings deny good hands, making the rest of the auction simpler.

 After the strong 1 opening, the main responses are:

  1=0-7 any distribution

  1/1/2/2=8+ Natural (5+ card suit and forcing to game)

  1NT=8-13 balanced

After any opening bid other than 1, all bidding is natural/normal -- as it would be with any natural system. 2/1 GF is still used as are any other modern methods such as negative doubles, inverted minors (only diamonds in this case), Jacoby 2NT, Drury, limit raises, etc.   There isn't much need to worry about opener reversing or jump-shifting since he is limited to a maximum of 15 points.

The (slight) main downsides of Precision:

1) The 1 opener, while "natural," could be made on a doubleton and it is tough to find diamond partscores (on the flip-slide, you sometimes keep your opponents out of diamonds when they belong there!). 

2) If the opponents preempt the 1 opening, there is often a lot of guessing needed to catch up.

If I were teaching beginners, I would want to start them with Precision--the easiest-to-learn bidding system. But, this isn't practical as 99% or more of their peers will be playing "Standard."

As a testament to how good this system is, in my estimate, in 2007, 4 of the top 5 pairs in America used Precision!

To read more details, see the summary in Wikipedia.