What are the features and specifications of the Speedlite SB400 flash unit?

The Speedlite SB400 flash unit is a compact and lightweight external flash designed for Nikon cameras. It has a guide number of 21 meters at ISO 100, a flash coverage of 18mm, and a tilting head for bounce flash. The flash unit is powered by two AA batteries and has a recycling time of approximately 3.9 seconds. It is compatible with Nikon's i-TTL flash control system for accurate exposure.