Last week on my patio job, the chalk line faded before I could make the cut. I had to snap it two more times to see it clearly! Your double-snap idea saves so much hassle now.
Watched my buddy Mike snap a perfect line for a deck board last summer. He turned around to grab his saw, and the line was just gone, like it was never there. He spent ten minutes checking his eyes and the chalk box, thinking he was going crazy. Now he double snaps everything, even on short cuts, because that one time messed with his head so bad. Does the chalk just decide to quit sometimes?