一 is the indexing radical and acts as a measuring rod laid across the body of the char. It gives 丈 its sense of marked length - the unit (about 3.3 m) was originally measured by a man's outstretched arm, with this stroke as the yardstick.
又 pictures a right hand. Strict etymology reads 丈 as a hand holding a stick, both an instrument of measure and a symbol of the elder male - which is why 丈 also became an honorific for husband in compounds like 丈夫.
