By entering arrow data as required above and clicking on 'calculate' an estimate is made of the arrow FOC and two values the 'Response Coefficient'' and the 'Drift Coefficient' presented.

All the requested information re fletchings relates to a single fletching (three fletchings are assumed).

The 'Fletch Length inch:' is the length of the base of the fletching in inches.

'Fletch Distance From Front inch:' is the distance from the front of the
shaft to the front of the fletching in inches.

The **Response Coefficient** represents the angular acceleration of the
arrow (i.e. how fast it will straighten up) when flying at an angle for some
reason (bad tuning, wind gust etc.). The higher this value the better as
far as arrow flight goes.

The **Drift Coefficient** represents the arrow angular acceleration (Response
Coefficient) divided by the sideways acceleration when flyng at an
angle for some reason. This coefficient represents the drag drift sensitivity
of the arrow. The higher this value then the faster an arrow will stabilise, probably leading to a more 'forgiving' arrow and reduced group size.

FOC remains the best overall 'evaluator' for assessing arrow flight performance. The idea of the Response and Drift coefficients is principally to compare the performance of different arrows with the same FOC.

*Last Revision 1 July 2009*