Measuring Tools

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Tools and practical methods for measuring and analyzing precision.

2-Shot Method

Brent Danielson described a no-frills method for accumulating arbitrarily large shot sample sets for statistical analysis: Since our statistics all depend on the sample radius:

  1. Shoot two shots at a single aim point
  2. Measure their center-to-center distance. This produces two radius sample points, both equal to half the measured distance.
  3. Repeat this process until satisfied with the quantity of data points.

Calculation of sigma from Danielson's sample data, as well as hypothesis analysis, are shown in Media:DanielsonExample.xlsx.

OnTarget

Jeffrey Block's OnTarget Precision Calculator is the most convenient package for converting a target image into data points for analysis. It accounts for scale and distance and automatically calculates Mean Radius (called "Average to Center" in the software) and Extreme Spread (called "Max Spread").

The more expensive Target Data System can automatically identify and aggregate shots on scans of its specially-coded targets.

[shotGroups Analysis Package]

Daniel Wollschlaeger built this package for the open-source statistical environment R to analyze target groups with respect to their shape, location (accuracy) and spread (precision). The package works with point data exported from OnTarget.

To get started:

  1. Install R from http://cran.fhcrc.org/
  2. Install RStudio from http://www.rstudio.com/ide/download/desktop
  3. Open RStudio, and in the console window
    • Run install.packages("shotGroups") to download the latest version of shotGroups with all dependencies.
    • Now run library(shotGroups) # load the package
    • Now you can run the examples. In RStudio all output diagrams will be displayed in the Plots tab:
      • example(groupSpread)
      • example(groupLocation)
      • example(groupShape)

For more, see the package description, the complete manual for all functions, or run help(package="shotGroups")

Spreadsheet Analysis

Given a target data set, whether compiled using the #2-Shot Method or #OnTarget, all of the analysis described here can be performed using standard spreadsheet functions. See, for example Media:CCI 40gr HV 100yd.xlsx or any of the other workbooks linked in the Examples.