What is the difference between the Marlin-P and the Marlin?

The Marlin-P is designed for indoor pool use and does not contain a Global Positioning System (GPS) module. It can only be set to pool mode. The Marlin has the all the features of Marlin-P plus an open water mode which uses the GPS for navigation and distance calculation when used outdoors. The Marlin is yellow-greenĀ and while the Marlin-P is blue.