When one person reels in their chalkline, it also brings in the hook from the other line, loading it with chalk on the way.
We recently had to snap chalklines on a roof to mark rafter locations. Rather than scramble back and forth across the roof, we tied the hooks of two chalklines together and worked as a two-person team. When one person reeled in their chalkline it also brought the hook from the other line to them, loading the line with chalk on the way.
— Seth Vasser, Washburn, Wis.