IBM/PC Interface is a 9-pin-female RS232 serial port to 3.5mm stereo jack. This kit includes a 4-foot patch cord with 3.5mm stereo jack plugs on both ends. One end of the patch cord plugs into the stereo jack on the Beta, Beta Master and Gamma, Gamma Master Chronys; the other end of the patch cord plugs into the stereo jack of the IBM/PC Interface. In conjunction with our Chrony Ballistics II Software, the IBM/PC Interface lets you download all of the data stored in your Chrony memory into your computer. This data can be automatically downloaded into a file on your computer for further manipulation by our Chrony Ballistics II Software programs. With Chrony Ballistics II Software, you can generate charts and graphs, calculate down-range performance, et cetera.