Measuring Groups

[Aussie_bob]

Can anyone tell me the name of the Gizmo that attaches to your verniers to measure Groups accurately?
It is a perspex arrangement with projectile dia Circles engraved on it etc and also who sells them.
Thanks in Advance.
Bob

 

[Kodiak99317]

Neil Jones makes one.
http://www.neiljones.com/html/target_measuring.html

For your own personal use, I would go with a Hood Kwik Estimator...
http://www.benchrest.com/hoodpress/kwik_estimator.html