If a label starts with a number the coco interpreter doesn’t throw an unknown label error like it does if it starts with a letter. When I made all characters significant before I didn’t address this issue. They could have said go to 1 and they would have been surprised by the results. I keep the number of screen lines for the logical file line in the number field, so there is probably a line with a 1 in the number field. It’s good that it has shown up here, so I can fix it properly. I’ve just come up with the ultimate solution. The coco screen has reverse digits available. I should check it, but I think that the basic interpreter will catch it. The process works. There’s a hook before the user enters a line. If I change the ‘0-‘9 to $60-$69 they show up as inverse ‘@-‘I in the normal basic listing. When the basic interpreter comes across them it sees them as zero and throws an unknown line exception. Of course I call it unknown label. There’s a hook for before a file line is put on the screen. So, I can change them to inverse ‘0-‘9 when I put them on the screen.