Ah - a clue there - thanks Wesley. It looks like what's called the Nashville system, which uses numbers to indicate the chord in any scale - 1=C, 2=D. etc., in the key of C. The two numbers underlined together seem to indicate that they are in the same bar.

The system, using Roman numerals instead of Arabic, has long been a convention in jazz progressions = I, IV, V, etc. - just never seen it done this way before.