The graphs show the stability as a function of leaning - doubles with a total weight at 400 lbs, Black Pearl and Jehu at 220 and the other at 245 lbs. The calculations are made with the gravity center at 20 cm above seat surface - meaning that the graphs can be used to compare these kayaks only - not with the measurements in f x Sea Kayaker, that uses 25 cm height. The reason for using a non-standard height is that some of my kayaks (Njord, Hunter, Black Pearl and Jehu) would have had negative stability, rendering the presentation useless. If the result of the standard calculations were to be believed, these kayaks would capsize all by themselves. They don´t. The choice of 25 cm was a convenient convention at a time when the norm was a wide recreation kayak. Since then kayaks have become narrower. Apart from that, the calculations are not very good at representing a living and moving paddler - they suggest a rigid paddler glued to the seat and with an iron rod as spine. Do not believe everything that comes out of the computer.
This is how the graphs can be interpreted. The are between the graph and the baseline is the total stability. The left part of the curve show initial stability - more the steeper. The curve to the left of the peak indicates secondary stability. The peak itself show how much the kayak can be leaned without tipping over. The curve to the right of the peak is hardly usable - you cannot balance on a declining stability.
Thus the graph indicates that an Isfjord have more initial stability than a Norton, but the latter have more secondary stability, and can be leaned slighly more without going over (it therefore takes a little more to rolla). Furthermore you can see that Jehu, Black Pearl and Hunter are approx the same in initial stability, but differ i secondary.