The Base Unit Upgrade Kit allows the use of the Base Unit, Model 91000-4, with a USB interface instead of a serial link. The Upgrade Kit consists of a cable with a USB connector at one end and a DB9M connector at the other end. The kit also comes with a CD-ROM (Model 39167) providing the required drivers for communication with the Base Unit. A readme file explains how to install the drivers. With this kit, users are able to use the Base Unit, Model 91000-4, with their current version of TechLab.