Tap target

This tool answers a simple question: where did my arrows land, measured in millimetres, and what shape is the group? On the screen there is a 122 cm face drawn to scale. You look at the target, put your finger on the matching spot and lift it when the crosshair in the magnifier sits on the hole, one arrow after another and in the order you shot them. Once you have marked the end or the round, press Calculate: below you will find the score, the group centre, the spread and the working, step by step, with your own numbers.

Everything stays on your device. The page sends nothing over the network: the arrows are kept in the browser until you press "New round", so download the CSV before you change phone or clear your browsing data.

How it works

The target on the screen works in real millimetres, with the origin at the centre: x grows to the right and y upwards, as on graph paper. When you put your finger down, a magnifier appears that enlarges the area under your fingertip five times, with a crosshair in the middle. It is there because on a phone the 122 cm face shrinks to a few centimetres across, and the tip of your finger covers exactly the spot you want to mark. You slide until the crosshair sits on the hole and lift: at that moment the arrow is recorded, with its coordinates rounded to a tenth of a millimetre. If you lift your finger outside the square, the touch is cancelled and nothing is kept. While your finger is on the target the page does not scroll; to scroll, touch outside the target.

Each arrow gets a shot number and an end. The end closes by itself when you reach the number of arrows you have set (6 unless you change it), or you close it yourself with "Close the end". "Undo the last one" removes the last arrow marked and reopens its end. Arrows in the current end are black and numbered; those from earlier ends are grey.

Some arrows have a score but no point: a bounce-out, a pass-through, a lost arrow. With "Arrow without a point" you record them with their shot number, the ring read on the target and the reason. They count towards the score but not towards the centre or the spread, because they have no coordinates. If you prefer the keyboard, or already have coordinates measured some other way, you can type them in "Enter coordinates by hand": they count as a tap.

When you press Calculate, the tool runs the same sums as the analysis engine it comes from. The score comes from how far each point is from the centre: X up to 30.5 mm, 10 up to 61 mm, then one ring every 61 mm down to the 1, which reaches 610 mm. The group centre is the average of the x and y values. The spread is the standard deviation of x and of y around that centre, taken on each axis separately, and their ratio sums up the shape of the group. The 90% diameter is twice the distance from the group centre that holds at least nine arrows out of ten, read from the arrows you marked rather than from a model.

How to read it

The group centre tells you where you are shooting on average; the spread tells you how consistent you are around that point. They are two different things and are best read separately: a tight group that sits off centre calls for a sight or tuning correction, while a centred but wide group is about execution. As a rule of thumb, if the centre stays more than 15-20 mm away from the middle of the target over several sessions, the correction belongs on the sight or in the tuning; one session is not enough to say so.

The two standard deviations tell you how wide and how tall the group is. Their ratio, vertical divided by horizontal, sums up its shape, and here too the cut-offs are rules of thumb: above 1.12 the vertical error weighs more, and the usual first place to look is whatever moves the arrow up and down, such as the release, the draw length and the clicker; below 0.9 the horizontal error weighs more, and you look at alignment and bow torque. Between the two values the group is roughly round, and the shape alone does not point in any direction.

The 90% diameter is the easiest figure to picture: it is the circle that holds almost the whole group, and it is the number to compare from one session to the next, at the same distance and with roughly the same number of arrows.

The score, finally, is a check. The ring next to each arrow is worked out from the coordinates, taking the marked point as the centre of the hole; the official ring is still the one read on the target. In the list, arrows with the note "check the target" are within the tolerance of a line, and those are the ones to look at again.

Under the results, in the box "What your numbers say", the tool reads your round back against these same rules: where the centre sits compared with the 15-20 mm, what shape the group has, whether it tightened or opened up between the first and second half of the round, and how many more arrows you need for a reliable reading.

The CSV file

The CSV has one row per arrow, in shooting order: shot number, end, x and y in millimetres, the ring worked out from the coordinates, whether it is an X, whether it is within the tolerance of a line and, for arrows without a point, the reason. In those rows the coordinates stay empty, not zero. The separator is a semicolon and decimals use a point; if your spreadsheet uses a decimal comma, choose the point as the decimal separator when you import the file.

Limits

The precision is that of a finger on a screen, helped by the magnifier, plus the eye of whoever is transcribing. How many millimetres that comes to on the real target has not been measured: the 10 mm offered as the tolerance is a rough estimate, not a measurement of your finger. Without the magnifier the error is much larger, because on the scaled-down face a fingertip covers more than one ring. If you measure your own tolerance, for instance by marking several points whose position you already know, enter it in the settings and the arrows to check will update.

Precision of this order is enough for the size and centre of the group, and for following how the group moves from one end to the next. Millimetre-level work, such as how the group responds to a single sight click or what the wind does to a few arrows, needs a photo or scan of the target measured against reference marks. With the same uncertainty, an arrow close to a line could belong to the next ring, which is why the official score stays the one read on the target.

The number of arrows matters too. The shape of the group, meaning the axis ratio and the offset of the centre, is indicative from about 12 arrows and reliable from 30 to 70; with a single end it is mostly chance, and it should not be used to change your technique. Up to ten arrows, the 90% diameter is set by the arrow furthest out, and so by the whole group. These arrow counts, like the cut-offs of 1.12 and 0.9 for the axis ratio and the 15-20 mm for the offset of the centre, are rules of thumb from the guide the tool grew out of, not measured values: treat them as a guide.

The tool only looks at where the arrows landed. It knows nothing about wind, fatigue or equipment, and it treats every arrow in the round as shot under the same conditions: if you changed something halfway through, start a new round. The round also lives only in this browser: in a private window, or if you clear the site's data, the arrows are not kept, and that is what the CSV is for.

When you have no phone to hand, you can mark the arrows on paper with the plotting sheet and copy the points in here later. If all you have is the ring counts, the group size calculator estimates the size of the group. To find out whether a change in score across several rounds is bigger than chance there are the floor calculator and the score gap calculator; the other tools are on the Tools page.