Arrow deflection - direction of motion or orientation?

[Alex319]

The Book of War says that an arrow hit only counts if the head deflects more than 30 degrees. Does this refer to the change in the direction of motion of the head, or the change in the orientation of the head?

If it means the orientation, then this makes no sense because if you hit a target square in the chest and the arrow bounced straight back, it wouldn't count as the orientation doesn't change (much).

If it means the direction of motion, it seems that this is very difficult to judge because when you hit a target and the arrow continues past him but starts tumbling (or sometimes just oscillating), then the path traced by the head is a combination of linear motion and rotation, and so will look something like a curtate cycloid http://en.wikipedia.org/wiki/Cycloid and it is almost impossible to tell what the angle change was at the moment of impact.

It would make more sense if the "deflection" was just measured as the change in direction of motion of the arrow's center of mass. This direction will only change when external force is being applied to the arrow (i..e at the point of impact) so it is much easier to judge by just looking at the angle between the shooter, the target, and where the arrow lands.

Or am I completely misunderstanding everything?

[Big King Jimmy]

You're reading too far into it and thinking about it to much, this rarely ever actually comes up on a national field. But it's direction of motion. It's not that hard to judge in combat.