I have one that served me well for fifteen years. Many of those years I didn't use it at all, but it worked fine for the last several. Until I tried to upgrade the memory. There is a slot for memory expansion, and the manual said it would work with any generic chip. It didn't work with one a friend loaned me, so I purchased one for $100 from Calcomp. That didn't work either, and I damaged something so that the control buttons didn't work. Then it stopped responding to plot commands at all. I gave up and purchased an HP111, which is a different topic.