Sights: adjusting for tournaments
Ferdinand Wegrostek dives deep. Very deep.
Asubtle job
Most publications describe in which direction the bow sight should be adjusted in case of arrow deviation from the center (called offset or deviation) based on an arrow group. Here a usually bigger problem for the archer should be discussed, namely when the archer should readjust the bow sight in a tournament, i.e. after how many arrows, and then by how much it should be readjusted.
The trivial answer to the question 'when', is first of all when the archer is reasonably sure that the centre of his arrow spread has moved from the center of the target face. To recognise this, however, it usually requires a few arrows, where a loss of score must be accepted. How many arrows should be observed? Are there also situations where the bow sight should be readjusted after the first arrow? Because if the basic bow sight adjustment is changed too early, it is possible that the bow sight has been wrongly adjusted and the arrows following on it group outside the target centre.
The archer is therefore in a dilemma: the bow sight (grain, ring) should be adjusted as early as possible, especially in a tournament, but there is a risk of incorrect adjustment with subsequent loss of score points. If the archer only reacts after sighting a few arrows, he has already lost score points.
It is also common to consider whether changed circumstances, such as an approaching wind, could have caused the unexpected deviation from the centre of the target or whether the arrow strike is still compatible with the archer's skill level and it was just not such a clean shot. One must then decide to either shoot more arrows to clarify the issue or to readjust the bow sight immediately or to practice aiming off.
If the archer has already decided to readjust his bow sight after the first arrow, the next question arises, namely by how much the bow sight should be readjusted. He does not know the center of his new arrow grouping after the 1st arrow. Should he correct the bow sight adjustment by the full distance of the arrow deviation from the center of the target or to only a part of it?
This article derives from a stochastic (probability-theoretical) point of view of practical procedures for the archer, trying to ascertain when at the earliest and by how much the bow sight should be reset or adjusted in a scored competition.
Attention:
The scoring ring 10 reaches from the beginning of ring 10 (border 9) to the centre of the target face (= 11). Ring 10.0 = beginning of ring 10, ring 10.5 = middle of ring 10, ring 11 = end of ring 10 (i.e. the centre of the target face). The same applies to the other rings!
Green marked is the hit area for which there is a probability of 5% and less. The column on the right shows the corresponding ring values for the 95%/5% limits.
As can be seen from the table, an archer with the skill 85 (WA 70: 1230) will rarely shoot a 5 or even 4 ring in a WA 70 tournament. Ring 6 has a probability of only 3.7%, ring 5 only 0.7%, ring 4 only 0.1% (=1 arrow of 1,000). The 5% ring limit is at ring value 7.1.
If the 1st arrow hits outside of this 5% limit, it should at least be a reason to rethink shooting technique, external factors and the bow sight setting or to readjust the bow sight if necessary.
The archer can take from table 1 the value for the 5% (95%) limit corresponding to his skill. Values for intermediate levels of the skill can be interpolated.
The values can also easily be calculated by yourself: 2 times average ring score per arrow minus 10.
The basic bow sight setting
The starting point for every tournament and training in which performance scores are recorded is a well adjusted bow sight. Usually at least 1-2 dozen arrows are shot in a row under good conditions (weather, archer) and the arrow grouping is considered. The lower the skill of the archer, the more arrows are necessary for a proper sight adjustment.
If the bow sight is not adjusted precisely, the scatter of hits is not in the centre of the target but, as shown in the example sketch below, away from it. In a group of several arrows shot, the optical mean or the socalled median is the reference point of the offset of the arrow group.
The median of the arrow group is mathematically the mean value of the horizontal and vertical values ordered by size.
In archery practice, the median is the optical center of the arrow group. It divides the 8 arrow hits into 4 hits above, 4 hits below, 4 hits left, 4 hits right. The vertical and horizontal arrow offset is then the vertical and horizontal distance of the median from the center of the target.
In the given example, the median is at ring 7 (exactly 7.5), approx. 8 o'clock.
The offset is the same vertically and horizontally and extends from the centre of the disc (11) to the centre of ring 8 (8.5). After this offset, the sight is adjusted horizontally and vertically by 2.5 rings each (from 8.5 to disc centre 11).This brings the median of the arrow group to the centre of the target.
Adjusting the bow sight already after the 1st arrow Yes or No?
is different, however, if additional information is available and the required conditions are met:
Requirements for the bow sight correction after only one shot:
1) The shot must have been faultless from the archer's point of view 2) There must be a recognisable (usually external) cause for a directional deviation from the center(misalignment), e.g. wind, rain, shifted "string shadow", changed anchor point, etc.
3) The arrow offset - measured by the skill of the archer - should normally be large and the expectation probability for this should be very low, about 5% and below.
If the conditions mentioned above are fulfilled, the archer should correct his bow sight after the first shot.
The light-green curve corresponds to an exact basic bow sight adjustment to the center of the target.
In the example almost all arrows are on the target (miss only 0.1%). The median runs at ring value 7.8, the 5% limit is at ring 4.2. Assuming the 1st arrow was shot with a good feeling and lands on ring 3 (exactly 3.5); 3 o'clock (orange circle). This is far outside the average shooting range. Because such a ring hit (and even worse) has only a probability of 4% (ring 3 = 2.5% plus ring 2 = 1% plus ring 1 = 0.4% plus Miss = 0.1%; see table). The archer attributes this significant arrow deviation to wind.
The wind has thus shifted the original hit distribution in the basic bow sight setting (green curve) to the right (pink curve). The question is: by how much really? You make the slightest mistake if you assume that this single first arrow corresponded to the average skill of this archer, defined by the median of his skill distribution.
Therefore the starting median is placed above the 1st arrow hit (at 3.5). Because this was the ring expected with average probability. The bow sight setting is corrected by the distance 1st arrow hit (3.5) to the median of the bow sight basic setting (7.8), i.e. by 4.3 rings.
Thus the important axiom applies: The bow sight should be readjusted after critical deviation of the 1st arrow from the center of the target face to the ring of the target face, which was to be expected with average probability for this first shot. This is statistically the median (central value) of the skill-related hit dispersion of the archer.
An estimate of the median is obtained by adding the value 0.6 *) to the average arrow score.
(However: if misses occur, the median calculated from the Ø ring value becomes increasingly inaccurate! This concerns especially archers with lower skills and the "difficult" distances like 50m, 90m and 18m indoor in the general class. Here the usual median calculation is recommended.)
This table shows the precisely determined medians:
Every archer can take from table 2 the 5%-limit and the median corresponding to his performance level, keep it in mind and act as the following examples show! Or he can quickly calculate the values himself according to the formulas given above.
Examples of readings
An archer with skill 60 (WA 935; WA70 236; av. arrow score 6.6) starts with a first arrow ring 4 middle (=value 4.5). This arrow is within the 95% probability limit (=value 3.2). There is also no apparent cause for this arrow offset. He should therefore not adjust the bow sight and shoot a second arrow for clarification.
An archer with skill 95 (WA 1298; WA70 323; av. arrow score 9) starts with the first arrow in the middle of ring 7 (=value 7.5). This arrow is outside the 5% probability limit (=value 8). After checking the two other prerequisites, he should immediately correct his bow sight to the middle of ring 9 (9.6).
"IS THERE NOT AN EASIER METHOD OF CORRECTING A SIGNIFICANT OFFSET OF THE FIRST ARROW?"
Bow sight correction with the halving method
The reader, who has followed the previous theoretical discussions with mixed feelings, asks himself: Is there not an easier method of correcting a significant offset of the first arrow? A method which also leads to an acceptable correction result without much thought and which can be easily applied by all archers?
Well, it exists, but with limitations. It is the halving method – halving of the arrow offset. Simply halve the distance of the strongly offset arrow to the center of the disc.
Rule of thumb for the halving method:
(disc center [11] + exact ring value of the offset arrow)/2