I've only come across one problem with the program. I stored a string into a “?” variable, then grouped it with a couple other variables. When the calc wouldn't stop adding the string to itself, I removed the batteries, and now the majority of the data I had on my calc has disappeared. I believe they are still there, but I cannot find them, and I can't use “Omnicalc” to restore them. That would be my only warning: don't use the “?” variables. They're marked as "?" for a reason.