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There are adapted conventions to pressure measurement, i.e., pounds per 
square in the British system and mm of Hg in the metric system. The 
force ( and force is the critical number since it is force that has to 
be balanced) on the back is related to pressure is given by the pressure 
over an area of the back times the surface area of that portion of the 
back. So much for the physics - the important issue is what does this 
mean to the physiology of the horse and at what force (or pressure) does 
muscle damage begin and is this uniform over the back, e.g., is the 
wither more susceptible to damage than the large muscles in the middle 
of the back to the same pressure? Given that all forces have to balance 
on the horses back - i. e., the horse has to hold up the rider and 
saddle, the horse will undergo all the weight (force) of the rider and 
saddle.

There are additonal forces that arise from the horses gait - that is the 
acceleration when the horse is lifting up in the trot is translated to a 
force on the horse's back.

This may mean that there has to be a trade off required if force cannot 
be evenly distributed over the horse's back.That could happen in the 
case of a heavier rider where the total force could be too large to be 
distribute evenely over the back. This I think is critical and probably 
a missing link. Until the physiologist or vets can specify just how the 
pressure should be distributed over the back - where it has to me 
minimal and where it can be more - numbers will be nice but there 
utility will be somewhat limited.

An additional factor is heat. Heat can play a factor and heat can 
destroy tissue as well as pressure. So to get a complete picture - an 
idea of heat distribution would be very useful. Heat is also critical in 
the senor design and selection of sensor material. Many (but not all) 
materials change electrical properties as a function of temp. Strain 
gauges (mini Wheatsone bridges) and piezo-electrc devices being two such 
materials. Therefore in order for the pressure measurements to be 
accurate using such a material, the tempurture at the sensor needs to be 
measured and the raw pressure measurement corrected for the biasing 
caused by increased heat.

Piezo-electric devices also have the properity that they change voltage 
based both on direct downward pressure and deflection pressure (bending) 
so somehow the raw pressure reading would need to be corrected to remove 
the deflection pressure bias since these sensors tend to be stiff ans 
will be deflected when put on a curved surface.

Cheers,
Truman

Robert Ferrand wrote:

> Ride Camp,
>
>
> The point I keep trying to bring to the surface is Measurement by
> definition, requires “a unit of measure” that can be related to a standard.
> This in turn requires numbers. If you cannot meet these requirements, it is
> not measurement. You should not call it measurement, when it is not. We have
> an English Language, we should use it correctly. Measurement means
> measurement. There is no way around it.
>
> Now, there are a lot of advantages to numbers. The horse could be measured
> and then a computer controlled router could be programmed to make calibrated
> saddletrees that fit, how is that for an idea?  Saddles could be measured by
> saddle makers and then you measure your horse, and then go to a database and
> only purchase a saddle that meets those measurements, so it fits. Way cool
> idea, eh what.. Numbers are a good thing. There is no reason to be afraid of
> numbers.
>
>
>  



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