A "mill" is distinguished from normal typewriters by having all caps (9 point, sans serif) and having numbers "1" and "slashed 0" on the top row. Note: Portable models were typically used elsewhere than in the radio room, but still have the same key/type layout.

In paper books I use Cal Newport’s “Morse Code method” placing a dot in the margin by a main point and a dash in the margin by a supporting point.