The curly quadrant tool is most useful for data that exhibits spread and for use with with FMO controls. 
A curly quad is a non rectangular gate based on the error profiles of photomultiplier tubes (PMT). Each compensated fluorescence parameter in an FCS file has a bivariate detection limit represented by the formula p2=a*p1^0.5 +b, where p1 and p2 are the two parameters in the plot, and a is a parameter modeling curliness from secondary PMT noise, and b models background fluorescence. Mario Roederer wrote a paper on this effect, it is linked here.
Select Curly Quad from the Graph -> Gating Tool menu. Adjust the curve of the X or Y gate lines by clicking anywhere within the plot (not on the gate lines). Handles will appear for moving the gate lines and gate vertex.
When you click on the graph it will display the frequencies of events within each quadrant (these frequencies are the percentage of events falling within each quadrant, with respect to the events that fall in the current subset.
You may click on the central, shared vertex of quadrants to move all four simultaneously.
When you have quadrant gates on a graph, they cover the entire area of the graph at all times. This means that other gates may be below these gates. To select other gates, press the shift key while clicking on the desired gate.
To get quadrant statistics, simply add the appropriate statistic to each of the quadrants. For instance, you could select the first quadrant in the workspace window, and add the Frequency of parent statistic to get the percentage of that quadrant's subpopulation in the parent population. Click-and-drag this statistic to each of the other four quadrants. (Or, select all four nodes before adding the statistic).
