What's the name of what Nami is wearing on her wrist? It is used to measure the weather.

Nami's forecast of the weather is based on her years of work for pirates, her own talent and years of research. Has nothing to do with the permanent pointer in her hand. The permanent pointer is used to point out the direction of the island. It will always point in the direction of the island until the records on the island it refers to are full, and then it will point in the direction of the next island.