Each complete turn of the big pointer (red) corresponds to a fraction of turn of the small pointer (black). The number of turns of the red pointer, to make the black pointer to carry out one complete turn, is the ratio of the indicator.
Example: a ratio of 12:1 means that 12 turns of the red pointer correspond to a complete turn of the black pointer (fig. 2). 12 turns of the handwheel cover the entire setting range. For each turn of the handwheel, the black pointer indicates 1/12 of the entire dial.