WHEN we walk into our local tack shop most of us are confronted with a confusing array of bits in different styles and materials. No wonder they are among the most misunderstood pieces of horse equipment ever invented.

All too often, we think that because the horse is a big animal, the pressures needed to control it must be big. That's a myth. All a horse needs are tiny pieces of information with the right timing to get the response we need.

There are very few surfaces where the bit can apply pressure. So it takes some pretty complex applications of pressure to those few points to create complex communication.

There are seven points of control that the bit can work on. These are the poll, the nose and the curb groove, the corner of the lips, the upper and lower bars, the tongue and the roof.

The bit must be shaped in such a way and fit properly within the mouth so the horse is able to understand what the communication is. Therefore a bit must be both directional and horse logical. Needless to say, it must not cause any injury that will result in temporary numbness.

The area in the horse's mouth where a bit communicates our pressures most effectively to the horse is called "the bars". These gaps between the front teeth and the back teeth on either side of the jaw consist of tissue-covered, pressure-sensitive cartilage. The bit lies across the bars and presses against the tongue. Depending on its shape and adjustment, a bit can also put pressure on the lips and on the roof of the mouth.

Pressures on the lips are the least effective because they are an unstable surface and easily injured.

The first thing to look at is the bit's contact area. When trainers talk about "pounds of pressure" on a bit, they are really talking about pounds per square inch of pressure over this contact area. The thinner the bit, the less contact area it has and the greater the pounds per square inch of pressure - or, in other words, the more noticeable any pressure on the bars will be.

With a thicker bit, the same amount of rein pressure will be less noticeable. So the effective size of the mouthpiece is the first thing to look at because it will determine how noticeable the pressure you apply will be. Rough bit surfaces such as twists reduce the area where pressure is felt much like rough tread reduces a tyre's surface area where it meets the road.

The second thing to look at is whether the mouthpiece is straight or shaped. If it is straight, the tongue absorbs some of the pressure and the horse will feel less pressure on the bars.

If the mouthpiece is hinged or grooved so it relieves pressure on the tongue, the bit is more noticeable on the bars and gives more directional guidance.

The third thing to look at is leverage. The way to determine leverage is to measure the distance from the mouthpiece to where the reins attach, then compare it to the distance from the mouthpiece to the curb chain (or strap). Most curb bits have a 3:1 leverage ratio. That means if you put 10 pounds of pull on the reins, the horse will feel 30 pounds of pressure squeezing his mouth.

Leverage decreases the amount of time it takes for the horse to feel bit pressure. If you have a bit with 3:1 leverage, the horse feels 10 pounds of pressure three times faster than he would if you applied ten pounds of pressure with a non-leverage bit like a snaffle.

To make this kind of bit pressure understandable and horse logical you'd have to soften the pressure to reward the horse three times as quickly as you would with a non-leverage bit. Because of this exaggerated pressure and release, curb bits impede true feel and understanding between you and your horse.

Curbs are also non-directional. Their pressure is felt as a clamping between the horse's chin and the bars of his mouth, and therefore can convey minimal direction to the horse.

If you use a chain, the pressure is more noticeable underneath the chin. If you use a thick leather strap, the pressure is more noticeable on the bars of the mouth. In most cases, curb bits are used as a signaling device rather than as a training device to help the horse learn to shape himself correctly.

The comfort and welfare of your horse or pony is of prime importance when you decide which bit and bridle to choose.