Two Points Determine a Line
Any two distinct points in a plane determine a line, which has an equation determined by the coordinates of the points.
When "grid" is chosen to be "integer", the locator points snap to integer coordinates on the grid. This tends to simplify the coefficients for the equation. When "grid" is chosen to be "open", the coordinates and coefficients in the equations are given to as many as five significant digits.
When "coefficients" is chosen to be "rational", the coefficients in the equation are rounded to a nearby rational value. High school students often have a preference for decimal coefficients over rational ones, even though exact rational ones are usually more useful. Within the visual accuracy of the graphs, the rational coefficients can be considered exact.