Let me say first of all that this is not intended to be a discussion of how we build arrows of a given spine. It is about a reliable method of assessing how a given arrow shoots out of a given bow.
It is a fundamental proposition that you can only meaningfully test anything in relation to shooting WITHIN your ability to shoot a meaningful sample, BUT this situation is ameliorated by taking note of the mean result from a larger sample.
First of all, testing for spine match is not shooting practice, so we are not concerned with shooting groups in the round.
We are only concerned with left/right alignment and the lateral error.
Therefore the target should be a narrow vertical line on a clean surface at the closest distance at which we can achieve clean arrow flight.
"Clean" flight is in this sense defined by recovery from paradox and no fishtailing with a clean loose.
I test for spine at ten or twelve paces but you should find and shoot from the closest distance at which you can consistently achieve clean arrow flight and recovery from paradox.
When it comes to executing each shot, concentration should be upon precise alignment with the vertical line, consistent draw length and a clean loose.
It is acceptable to discount very obvious gross shooting errors, but resist the temptation to tidy up your results, since the object is to find the mean centre of spread in lateral alignment.
If you do not line up systematically you can still get a mean result, but I try to shoot as precise and neutral a test as I can manage, but this will be a little more difficult to do consistently if you have a rather loose shooting style, which is why a large sample and a mean result is a meaningful way of conducting this test.
Do not try to shoot a group at a single spot, but stitch a line down the vertical line on the target then measure and record the distance of each arrow from the line.
This can be done by, for example, recording precise hits as a zero value and shots to the left as minus values and shots to the right as plus values.
An exact spine match should produce a result with a mean score of zero, and for a right handed archer, a result giving a mean score of a minus value indicates a stiff shaft and a plus value indicates a weak shaft.
With what I deem to be an acceptable match I would expect to hit the line with a spread no more than a finger width either side of the line, but the acceptable spread will be a matter of what you find acceptable at your present level of skill, but this is of no concern within the context of this test.
The mean value defines the spine match.
What is important in any equipment test is that the subjective element is reduced, if not entirely eliminated.
In any shooting test it is important to be able to clearly distinguish between what variables are generated by the archer and what diveregence is being generated by the equipment itself.
This might seem illogical since you cannot divorce the archer from the effect he will have on the bow, but in very real terms, it is vital in terms of being able to diagnose and effectively deal with what happens when you shoot.
With the archer we try to reduce and eliminate unwanted variables in form and execution, whereas with the equipment we seek to eliminate variables and to achieve a set up that is optimised for producing convergent or at least less divergent characteristics in arrow flight.
There are enough mediocre archers who think that they will improve by fiddling with equipment despite the fact that they do not understand what they are doing, or believe that they can make their problems go away by purchasing a gimmick or taking facile advice which they do not understand.
The only catch with this method is that if you are incapable of accurately lining up your shot and your alignment itself produces a lateral bias, then you will have a bias in the result.
It is not uncommon for example, that a carelessly aligned right hander will get a result defining a spinematch as being somewhat stiff, since a common error amongst right handers is to align the shaft slightly to the left of the mark despite having the point in line, not having the eye directly over the shaft.
Even more likely is that youtr shaft will tend to shoot somewhat to the left rather thanconsistently straight since it is unfortunately true that the majority of us have a less than consistently perfect loose and that any lateral movement of the nock end of the shaft (away from the face) will result in an error to the left at the target.
The majority of archers (and I have seen thousands) loose by flipping our fingers out in some degree or even take the hand away from the face with the result that lateral placement is inconsistent.
But performing systematic tests will in time have the benefit of making any but the most unobservant more aware of some of their idiosyncracies of form.
The only worthwhile solutions are to be gained by careful observation and the intelligent application of effort.