Here is a quick guide on how to do it.
How to snap a chalk line for roofing.
Hammer a nail or drive a screw into one of the end points.
Mark the two end points of the line you are trying to draw.
Pull the string loaded with chalk out of the chalk reel.
First shake up the chalk inside your tool or add chalk if it does not have any.
Stretch the chalk coated string tightly between the nails.
To pop long chalk lines accurately when flooring or roofing.
You can create a straight line over a considerably length without any lasers or high tech equipment when you know how to snap a chalk line properly.
Then hook one end of the chalk snap line to your beginning point.
You may need a measuring tape to set these points.
The end of the chalk line is tied to a loop or clip.
If you have a well functioning chalk snap line you can slowly play out the line without using the crank.
Hold or secure the chalk line at the end point of the line.
Find the endpoints of your line and drive a nail in at each point.