http://www.peterman.dk/windsurf-mast-article-gb01.htm
Bend Curve.

If you measure how much the mast deflects at the 1/4 point of the mast, at the midpoint, and at the 3/4 point you get some figures telling of the way the mast are bending under load (called bend curve or bend characteristics). If we for instance say that a mast deflects 13 cm at the 1/4 point, 20 cm at the midpoint, and 15 cm at the 3/4 point, you find your calculator and do as follows:

First you calculate how much the mast deflects at the 1/4 point in % from the deflection at the midpoint. In our example it's (13 x 100 / 20) = 65 %.

Next you do the same calculation for the 3/4 point - that is the deflection of the mast at the 3/4 point in % from the deflection at the midpoint. The calculation is (15 x 100 / 20) = 75 %.

Now all you have to do, is to subtract the two figures - that's 75 % minus 65 % = 10. To be correct, the denomination is not 10 % but 10 %-points. Anyway, you say that the mast has the bend curve of 10 *).

To make it easier to understand the bend curve figure you can translate the figures to these IMCS terms:



0 - 6: Hard top.

7 - 9: Hard top - constant curve.

10 - 12: Constant curve.

13 - 15: Constant curve - flex top.

16 - 18: Flex top.

19 - 21: Flex top - super flex top

22 - : Super flex top.