The "Delta" window selects the increment over which the independent variable is plotted. If you make it too large you will have a plot with poor resolution. If you make it too small you will end up with a noisy plot. (If you make it smaller than one pixel you will get a very strange-looking plot.) Also, there is a defined limit on the maximum number of data points, currently set at 2000. Note that if you are going make plots of a number of related data sets, you probably want to set the integration region and the delta to be the same for each data set.
The limits for the Line and Ellipse options behave somewhat differently from the others. For the Line option, the "Low" and "High" X- and Y-Pixel values are the coordinates of the two ends of the line segment. "Fract" is the equivalent of "Delta" for the other plots--the number of points will be 1 + 1/Fract. Pixels are included in the plot if they are within Width/2 of the line segment itself. So a Width of zero will in general not include any pixels at all. (The default is 3). It is suggested that for this kind of plot you will almost certainly want to Average rather than Sum the data. For the Ellipse option, the independent variable is always Chi and always goes from zero to 360; the dependent variables are the lengths of the semimajor and semiminor axes a and b (with however b being allowed to be greater than, equal to, or less than a).