chalk line devices are commonly used in the building and / or construction arts . the motorized chalk line apparatus is particularly useful for automatically reeling in a chalk line wound about a spool that is journaled by a pair of stub axles . a battery powered drive automatically winds the chalk line about the spool . in use , the chalk line is manually pulled away from the apparatus to create the marking , but when the user actuates the switch , the spool automatically rewinds the chalk line .