Notch
App of the Day
from the creators of 
murmur
Layered
How to measure a group
Find the two holes that sit furthest apart and measure across them, outside edge to outside edge. Take off one bullet diameter and you have the centre-to-centre size, which is the figure shooters compare.
Why the angle matters
A size only means something with its distance. One minute of angle is 1.047 inches at 100 yards, about 29 mm at 100 metres. One mrad is 100 mm at 100 metres. As an angle, a 25 yard card and a 50 metre card can be compared.
Or photograph the card
Notch measures the group and the spread from a photo, for every card in a session, and keeps your tightest grouping in your records.
Questions
How do you measure group size?
Measure across the two holes furthest apart, outside edge to outside edge, then subtract one bullet diameter. The result is the centre-to-centre group size.
How do I convert group size to MOA?
Divide the group size in inches by the distance in hundreds of yards, then by 1.047. A 0.63 inch group at 25 yards is 2.41 MOA.
What is the difference between MOA and mrad?
Both are angles. One MOA is 1.047 inches at 100 yards. One mrad is 100 mm at 100 metres, which is about 3.44 MOA.