The Flip Test

 Terry Hardaker & Stephen Dunn



The Flip Test is a new statistical test for assessing the symmetry of prehistoric stone tools, available as a free download on the Internet . The program is described by Hardaker and Dunn in a BAR (British Archaeological Reports) volume: Bond, C.J., (forthcoming), and in Antiquity, vol 79, no. 306, December 2005 .


What is The Flip Test for?


The purpose of the Flip Test is to provide a numerical measure of the symmetry (or asymmetry) of stone tools. Because bilateral symmetry is assumed to have been intentional in certain stone tools, notably the Acheulian biface or handaxe, symmetry can be considered as one of the measures of “quality” of a stone tool, and consequently of the skill of its maker.

There has previously been no simple and widely accepted means of measuring the symmetry of a tool. The Flip Test is proposed as a means of doing this, by measuring the “index of asymmetry” as a numerical value for each tool. Values will typically lie between 1.5 and about 6.0. The lower the value, the more symmetrical the tool.


How is the Index of Asymmetry Calculated?


The principle of the Flip Test, as implied by its name, is the assessment of the deviation from perfect symmetry by flipping the tool about its vertical axis and measuring the difference between the two superimposed outlines.

The index of asymmetry is calculated by


500 (A) 



where A is the asymmetrical pixel count, H is the maximum height and W the maximum width.


Downloading the Flip Test


The Flip Test can be downloaded on the link shown.

It can be freely distributed as shareware.

It should install and operate on Windows platforms from Windows 98 and later (inc. Win 2000 and Win XP). Please contact the authors if you experience difficulty with this - See “User comments and Feedback” below. Note that download of the Flip Test constitutes acceptance of the terms of the Commercial Use  and Disclaimer clauses at the end of this website notice.





Use of the Flip Test – Installation

Click on the  link shown to download the File “”. You can choose the location on your PC to download this file to.

When the download is complete, you will generally be able to “un-zip” it automatically by double-clicking on it - If this does not happen, you may need to download an “un-zipping” utility, for instance from


The File will un-zip to create 3 files, “”, “setup.exe”, and “setup.lst”.

Double-clicking on the “setup.exe” file will launch a standard windows installation process.


This will take you through the standard windows “Install” procedure;



Use of the Flip Test – Inputs


- The Flip Test currently works only on Graphics stored as “.JPG” files. These graphic files can be photographs or drawings of handaxes or other tools.

- JPG files should be:

·        “Dark on Light”, ideally a black or dark-grey tool pictured against a white or nearly-white background.

·        Devoid of additional detail - writing or other details should be removed

·        Top Upwards - The top of the tool should be pointing upwards.

If the tool is aligned on its side, the results will be meaningless.

·        Of size approx (100 x 100) to (400 x 400) pixels. If images are below the recommended size, detail is likely to be lost. If images are larger than this size the program will function correctly, but performance may be unacceptably slow, and the complete image of the artefact may not all appear in the window.


- If necessary, a graphic package such as PhotoShop can be used to prepare the graphic files before opening them in the Flip Test, for example to allow for rotation of images, re-sizing, adjustments to contrast, and removal of extraneous features.


Use of the Flip Test


When the Flip Test is opened, there are 3 initial options:

Open File - Auto Mode, Auto-Rotation

Open File - Auto Mode, No Rotation

Open File - Step-Through Mode


Open File - Auto Mode, Auto-Rotation

This is the default mode for using the Flip Test. The File-Open Dialogue appears. Select the .jpg file that you wish to analyse. The Flip Test will run through the procedures that are used to calculate the Index of Asymmetry, after which the Index of Asymmetry will be displayed in the top right of the interface.

When the Flip Test is run in this mode, the program will attempt to automatically rotate the image to give the “best” score, i.e. the lowest index of Asymmetry.


Open File - Auto Mode, No Rotation

The File-Open Dialogue appears. Select the .jpg file. The Flip Test will automatically analyse and report the index of asymmetry without rotating the image.

We suggest that you use this mode if you are confident that your images are already aligned at the “best” angle.


Open File - Step-Through Mode

The File-Open Dialogue appears. Select the .jpg file. The program will enable buttons allowing you to “step-through” the intermediate analytical processes, to produce the Index of Asymmetry. This includes a “Manual Rotation” option, which allows you to enter an angle of rotation to obtain the best result.


Some Comments on the Flip Test



Flip Test - Guidance on Outputs


As a rough guide, the following notes relating to Acheulian handaxe tests may be useful:



 Index of Asymmetry

Level of symmetry and interpretation



Virtually perfect. Suggests an almost mathematical level of precision has been applied - unlikely on Acheulian items - could it be a modern replica?


1.5 - 2.99

Very high. An exceptionally skilled craftsman - special purpose?


3.0 - 3.99

High. Skilled work


4.0 - 4.99

Moderate. Average work


5.0 - 5.99

Low. Look for intractable material, or eccentric shape e.g. on butt.


6.0 & above

Very low. Look for intractable material, serious material defects, eccentric shape or a modern break in the item



User Comments and Feedback


Although the Flip Test has been thoroughly tested, the authors welcome user comment, with a view to future improvement.

We can be contacted at




The Flip Test is intended for bona fide academic use in the study of prehistoric stone tools. Downloading the Flip Test Program constitutes acceptance that the user will not market, sell, or otherwise use the Program or any part of its contents for commercial gain and will not  supply the Program to any other person for such purpose.





The authors of the Flip Test provide the product "as is," and the authors of the Flip Test disclaim any and all warranties, whether express or implied, including (without limitation) any implied warranties of fitness for a particular purpose. In no event will authors of the Flip Test be liable to you or to any third party for any direct, indirect, incidental, consequential, special or exemplary damages or lost profit resulting from any use or misuse of this product.