Before a saddle fitter offers the range of saddles that he stocks , he gives the horse a thorough check by feeling along his back and monitoring the reaction. The application of gentle but firm pressure enables him to pinpoint any sensitive areas and assess the horse's muscle tone. The front of the tree and the points have to be at a similar angle to the trapezius area upon which they will rest. The tolerance level is certainly no more than 10 degrees. At this point, care must be taken to ensure that the angle is that of the tree and not of the fencing at the front of the panel, as these two angles do not necessarily coincide. If the saddle is too wide a fitting, there are two major problems for the horse and one major problem for the rider. First, the underside of the arch may well be in contact with the horse's withers. Additionally, there may be too much pressure exerted at the base of the arch on each side of the gullet.
 

With the saddle off load, i.e. without a rider on and without being girthed up, one should be able to slide one hand evenly and easily the length of the tree from the gullet to the point without undue pressure.
The next point is to ensure that the gullet is wide enough not to impinge on either side of the spine.  This is particularly important with horses with high withers, for example, aged thoroughbreds. However, this is where saddle design and fitting are very specific - while 'wide enough' is very important, 'too wide' creates a new set of problems. At the one extreme, with a narrow gullet, the edges of the gullet may clamp tightly each side of the vertebrae, causing extreme discomfort and trauma. However, a gullet which is far too wide must inevitably reduce the sides of the panel. That is to say, there is a far smaller area to support the weight of the rider and the greater the loading per square inch, the more chance there is of bruising.

How many fingers should fit between the top of the withers and the underside of the saddle arch?

The answer is that there should be sufficient clearance under load under all circumstances. It may well be three fingers. On close-contact saddles, it may be one and a half. Plainly, on a very deep seated saddle, there is likely to be rather more clearance than with a flat saddle, so one cannot be pedantic. In any event whose fingers are we talking about - a large man with fat fingers or a small girl with slim fingers?
It is essential that the saddle should sit in balance. This generally means that the candidate will sit slightly higher than the pommel. ‘In balance’ signifies that the rider can sit in the centre of the saddle, with weight divided evenly throughout the length of the panel.

The panel should fit evenly all the way through its length and breadth. If the panel is a correct fit it will utilize all of its area – as mentioned previously, the larger the area in contact with the horse, the less pounds per square inch of rider’s weight will be transmitted to the horse’s back. This should never exceed one and a half pounds per square inch at any point. This is where the type of panel is crucial.

The length of panel should not extend beyond the horse’s eighteenth rib.

Note that this does not extend vertically and therefore this measurement must be gauged directly underneath the rear of the panel.
This is an area which often gives problems, particularly when the horse has a short or dipped back and the rider is technically too large for the animal.

When the fitter is happy with the saddle, he will ask the owner to ride either in a school or open space so he can assess the horse in all paces. A good saddle fitter will always see the horse being ridden in a saddle.

While walking, the fitter will look at the saddle from behind to check for sideways movement which could cause bruising or hair loss.

The fitter will make the final check when he takes the saddle off. Scuff or sweat marks on the horse's coat will show whether the saddle has moved.

A good tip is to watch the downward transition from canter to trot. A happy horse will throw his scapula forward as he takes the first trot stride. A 'shambling' transition indicates a saddle which is too tight across the shoulders.

The fitter will keep a record of all his clients including a wither template and the horse's weight. This information helps him monitor any changes in the horse's shape or size.