We also have an earlier 21 machine with just yield monitor. We were recommended by Case 2 years ago to go with Adtron brand _Accent external reader for our PC. I think we hooked it up through printer port. The company is out of Arizona. They were very helpful. If this is your first time, you will find that several companies will tell you that their readers will work with no modifications. DON'T believe all of them. We tried 2 different ones before the Adtron worked. Even for it to work, we had to change a few command lines in the program. The company helped us walk through the steps to make it work. Good luck with your efforts, I can remember the challenges we went through to make things work.