From the Nielsen Kellerman site

The Kestrel® Interface is the ideal companion to any model in the Kestrel 4000 family. Whether you own a 4000, 4100, 4200 or 4500, with the optional computer interface, data can be uploaded for long-term storage, in-depth analysis and detailed charting.

This interface has the USB port connection 
 
Weight 16 ounces