The folding rule led to the invention of the modern tape measure. According to tool expert Bill Brockway, Anton Ullrich invented the folding rule in 1851. The invention of the folding rule “revolutionized jobsites, making it much more convenient to take construction measurements,” says Brockway. Folding rulers are essentially a collection of smaller rulers attached by hinges that allow the small rulers to be pivoted to rest on the top next ruler in line. These rulers can typically pivot together in a small package that fits in one hand. Typical folding rulers use American or metric measurements, though some use both. Typical American measure folding rulers are separated in 6- inch hinged increments.
Use a Folding Ruler
Hold a closed folding ruler in one hand.
Grasp the first segment on the top of the ruler and pivot it 180 degrees. Some folding rules click or lock in place once 180 degrees is reached. If this does not happen, simply align the segment with the remainder of the rule. A ruler nearly twice the size of the original segment is now in one hand.
Pivot this ruler from the second segment pivot 180 degrees to create a ruler nearly three times the size of the individual segment length. Continue in this fashion until the folding ruler is unfolded long enough to take the measurement desired.
Lay the unfolded length of ruler against the desired object to measure in a straight line. Align one end of the ruler with one end of the object.
Align the other end of the object with a fixed point on the rule and record the measurement indicated by this fixed point. Ensure measurement recorded is the correct measuring system if the folding ruler uses more than one system.