People often ask which masts will suit their sail or vice versa. I had been interested for a while to measure the bend curve of mine. I have followed the method described here www.peterman.dk/mast-imcs-formulas.htm although I only used 15kg. My findings were:
400 RDM C60 = 13.2%
460 SDM C60 = 15.0%
Which puts them in the constant curve - flex top category. Quite contrary to the chart on the Unifiber website that has been posted a few times recently. Hopefully this will be helpful to someone, or at least interesting 
I'll be getting a 430 RDM soon so I will measure that and add my results to this thread.
That confirms how my 08 naish masts rigged various sails, always felt-
460 freeride flexy in tip (really liked the feel of this mast)
430 100% rdm slightly stiffer in tip & than some other rdm's i've tried & really good for those used to sdm masts.
Why is that? Just for bigger numbers to reduce the amount of error, or does the curve change at higher deflection? 15kg was enough to get around 100mm of deflection at the midpoint, so my +-0.5mm with the tape measure wouldn't change the results enough to put them into another category. I set up a string line to measure to and used a plumb bob to make sure I measured square.
Probably cant make any conclusion out of one and only one mast measured... but interesting to see how it can deviate from spec.
Just speculating but you are assuming that the mast bend behaves as a constant regardless of how much weight is applied, I am not sure that is the case but I could be wrong.
The IMCS test is done with 30kgs, for you to have a set of figures that you can be confident of you should do the same test.
I have used my Naish 460 90% 2011 mast on my 2011 KA Koncepts a few times now and it felt fantastic with good top speed.
I have no idea what the % of the bend curve is (wish this was printed on more masts) but it feels very nice and works well along with setting the sail perfectly. I just got a carbon KA boom of AMAC after using alloy for years and it is sooooo nice and stiff.
Russ
Okay I did a pretty accurate test on my 2011 Naish SDM (Drop shape) 430 C90.
Middle deflection 179mm
Top Deflection 135mm = 75.4%
Bottom Deflection 117mm = 65.4%
Therefore it has a mast bend curve of 10 making it a constant curve.
IMCS came up perfect at 21.1
Will test all my other masts now I have devised a half decent way of suspending 30kgs off a mast pinned at both ends (there was some hesitation to hanging 30kgs off the mast and that somehow my back yard system would fail but alas it worked beautifully)
