I have never seen that version of the Mk 4 in my long aviation life. A fascinating find.
The normal airspeed line up the centre must be associated with altitude, and the concentric rings could be associated with airspeed, as that is the only thing you could do to the knot in those days. Winds were much less accurate.
But jumping from a helicopter was of such a rarity in those days that I cannot imagine they went to the trouble of producing a special calculator just to calculate the correct speed to fly with a specific wind and altitude.
To me an interesting mystery...