istDS and built in flash

Can anyone tell me if the built in flash on the istDS meters the exposure received by the subject and shuts down when the subject has received sufficient exposure, or must one always use the guide no. and aperture/distance calculation and manual settings.

The built-in flash uses P-TTL mode. Essentially, when you make an exposure with flash on, it actually fires twice (not to be confused with red-eye reduction) once to illuminate the scene for the camera to measure light levels etc, and a second flash for the actual exposure.