The range for the x-axis is either the interval [0,max] or [-max,max], depending on the setting of the "include negative" checkbox. ("max" is the value of the "max ka/pi" field.
The graph may be folded onto itself (using the "fold" checkbox); the graph will be folded onto either [0,pi] or [-pi,pi], again depending on the setting of the "negative" checkbox.
The "potential strength" field can range between 0 and 4, and affects the size of the discontinuities. Setting this field to zero will give the energy-momentum diagram for a free electron (this can also be displayed using the "free electron" checkbox).