When you construct a point to be on a line (or on a segment, or ray, or circle) in dynamic geometry, it is constrained to stay on that line; its location is dependent upon the location of that line, which can be dragged to a new location. [br]Use the “drag test” to check if a point really is constrained to the line: select the Move tool (the first tool in the Tool Bar, with the arrow icon), click on your point and try to drag it; see if it stays on the line. Drag an endpoint of the line. Drag the whole line. What happens to the point?[br]The drag test is one of the most important things to do in dynamic geometry. Make sure that everyone in your team can drag objects around.