## Why You've Probably Been Measuring Your Targets Wrong

Before TargetView, we used to measure the group-size of our targets by finding the two shots that were furthest apart and measuring the distance between them to obtain our group-size. At first glance, this seems reasonable. Those two shots are furthest apart, so that must be the size of the group.

But that's wrong! Below is a super nerdy explanation of why. Feel free to keep reading if you want to know more. Or, just trust that TargetView is measuring your targets correctly and accurately, and never worry about it again!

### Explanation

Figure 1 shows two shots on a target that are exactly 3 inches apart. The shots are labeled 1 and 2.

Figure 1

In figure 2, let's calculate the size of this two-shot group by finding the two shots that are furthest apart. This is pretty easy because we only have two shots! The size of this group is 3 inches. We can draw the group-size circle (in orange), just like TargetView does in the app.

Figure 2

Let's draw a circle with a 3-inch radius around shot 1. You can see this circle (in magenta) in figure 3. Any shot that lands within this circle will be less than 3 inches away from shot 1. It is also true that any shot within the magenta circle is at least as close (or closer) to shot 1 as shot 2 is.

Figure 3

Let's draw the same 3-inch radius circle around shot 2. You can see both magenta circles in figure 4. Any shot that lands within these two large circles is no more than 3 inches away from either shot 1 or shot 2.

Figure 4

Just like on a Venn Diagram, the intersection of the two large magenta circles represents a region where shots are no more than 3 inches away from both shot 1 and shot 2. This special region is colored gray in figure 5. Any shot that lands in the gray region will be less than 3 inches from shots 1 and 2.

Do you see the problem yet?

Figure 5

Let's clean up the drawing a little bit by eliminating extra lines. Figure 6 shows the special intersection region of the two large magenta circles. You can see there's a new shot (shot 3) on the target. Notice that shot 3 is not within the orange group-size circle!

Well, fine, that just means we have to redraw the orange circle. So let's start over by finding the two shots that are furthest apart, just like we did in the first step.

Figure 6

In figure 7, let's measure the distance between all the shots. Shot 1 and shot 2 are still 3 inches apart. Shot 1 and shot 3 are 2.73 inches apart. Shot 2 and shot 3 are 2.73 inches apart. So shots 1 and 2 are still the furthest from each other. So if we measure this 3-shot target, we would still get a group-size of 3 inches.

But this is wrong! If we draw a 3 inch circle on the target, shot 3 will be outside of this circle! You can see this clearly in figure 7. There is a 3 inch circle that connects shots 1 and 2. Shot 3 is outside of this circle.

In fact, any shot that lands within the gray intersection area will throw off the group-size calculation. Because: any shot that lands in the gray area is closer to both shot 1 and shot 2 than shots 1 and 2 are from each other.

Let's reword that last sentence: Any shot that lands in the gray area will be less than 3 inches away from shot 1 and less than 3 inches away from shot 2 and shots 1 and 2 will always be the two shots that are furthest from each other.

Figure 7

Let's draw the correct group-size circle in figure 8. The true/correct size of this three shot group is actually 3.27 inches, not 3 inches. TargetView knows how to do this measurement the right way, every time!

Figure 8

The worst-case scenario for error is shown in figure 9. If we place shot 4 all the way at the edge of the gray area, the true group-size is 3.46 inches. Technically, shots 1, 2, and 4 are all equidistant from each other. If you were to measure this target using the old (incorrect) method, you would still get an (incorrect) group-size of 3 inches. This is almost a half-inch of error, or an error of 13.3%! That's huge!

TargetView knows how to calculate the size of your groups *correctly* so you never have to worry. Your targets will always be measured correctly and reflect your true accuracy.

It's important to note that this explanation is not a recommendation to use 3-shot or 4-shot groups to measure the accuracy of your firearm or of yourself. 3-shot groups are not a statistically significant way to to access accuracy.

10-shot groups are for more representative of the true accuracy of a particular firearm, and 30 (or more) shot groups are even better.

Figure 9
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