That would be the international mast check system or (imcs) usually found printed on the mast for identification.
Elderly gents of windsurfing, the formula is: if partner unhappy, add more Viagra.
so carbon masts are, lighter, stronger, but should flex the same as a like rated grp mast?
A wet towel should give you a fair idea. Older masts have more curve when a wet towel is hung from the end.
