TPD on a watch winder stands for "Turns Per Day." It refers to the number of full rotations the watch winder makes in a 24-hour period to keep an automatic watch fully wound. Each automatic watch requires a specific TPD range that mimics the natural wrist movement needed to maintain its power reserve and ensure the watch runs accurately without stopping.

The importance of TPD lies in matching the watch winder's rotations to the watch's needs. If the TPD is too low, the watch may not stay wound and could stop; if too high, it could cause unnecessary wear, although most modern watches have mechanisms to prevent overwinding. Typical TPD requirements for most automatic watches range from about 650 to 1000 turns per day, but some models may need more or less depending on their movement and design.

Watch winders often allow users to adjust the TPD setting, sometimes in increments of 10 or 20 turns per day, to align precisely with the watch manufacturer's recommended TPD. This customization helps maintain optimal watch performance and longevity.

In summary, TPD is a critical setting on a watch winder that determines how many rotations it makes daily to keep an automatic watch properly wound according to its specific requirements.