Quick question about the PO-12 display

In the top right, when not displaying the time, the upper right corner will dsplay something like “1-03”. I understand that the “03” tells me what sound is currently selected. What is the “1” telling me?


I don’t know what it means, but that digit has only two segments, so it can only be a “1”.

Could it be letter “I” for “instrument”? Just my guess.

Thanks folks. Thought I was missing something, and had been meaning to ask for ages.