Left is my test piece. The typeface is Helvetica Light. Right is original Model M's. Letter spacing differs, but it isn't serious problem. A serious problem is 'g' letter. Compare the proportion of the upper part and the lower part. It differs much, and it is a strong evidence. Original Model M's typeface of modifier / system command keys isn't Helvetica family.
So what is the typeface? I cannot find it yet. I have a book, "Rockledge's classic international typefinder." This book contains many typefaces of 80's. But I couldn't find the typeface.
Around 1980, IBM was close to Monotype. So I guess the typeface is Monotype's unpopular typeface. I guess that it is made for photo-typesetter and not converted to font yet, because it is very unpopular.
By the way, the 'R' is very Helvetica-ish.
The tail of 'a' is Helvetica-ish too, but the head isn't so Helvetica-ish. From this earmark, I've doubted Monotype Abadi Std Light, but 'R' differs.
Another earmark is very short descender. Usually these earmarks are enough to find the typeface, but I cannot yet. This is a circumstantial evidence that the typeface was unpopular.
