Spa-Quip Davey new style in-pool temp sensor with 3m lead(also available in 10m Q915445-10). Fits with a mini din plug. Suits the following models: SP600 SP601 SP800 SP1200.
This sensor is not required as these models have a in-line temp sensor.
They are just used only if you would prefer to monitor the in pool temperature instead of the heater tube temp.
Most commonly used on a swim spa for a more accurate temperature.