Right after the pen is broken and Callum reports the tracking signal from it is lost, there's a shot which shows the tracker is still active on the screen behind him. It's even still moving.
The shots showing screens where Callum is triangulating the position of the calls show three elaborately decorated points forming three corners of a triangle, against a moving map background. But cellphone calls are triangulated by finding the cell towers in whose coverage areas the phone is active and comparing the relative signal strengths. Cell towers don't move anywhere, therefore the map wouldn't move, which makes those shots pretty but essentially meaningless.