#MEASURING TAPE USE PLUS#

Scientists in NIST’s tape calibration laboratory can measure a meter (3.28 feet) with a standard uncertainty of plus or minus 350 nanometers (billionths of a meter). Even more accurate tapes are available, such as those used for the Olympics or to measure the level of oil tanks, but they are more expensive.Īt NIST, researchers periodically verify the primary physical length standards that manufacturers use to print their tapes and other length standards used in industry. To be used for buying and selling goods, a 1.82-meter (6-foot) tape should be accurate to within 0.79 millimeters (1/32 inch), according to NIST Handbook 44, a sourcebook for many measurement standards. If the tape is accurate to within an acceptable tolerance, it passes the test, and the batch that it comes from can be sold. Scientists at NIST use a microscope to calibrate tape measures.Īs the microscope moves over the tape, manufacturers can compare the position of the hash mark on the tape with the distance reported by the interferometer. The measuring beam bounces off the reflector and rejoins the reference beam back at the detector. One of the beams, the reference beam, goes directly to a detector, while the other, a measuring beam, goes toward a reflector on the side of the microscope. Laser interferometers work by splitting a laser beam in two. The manufacturer aims the microscope at the tape’s hash marks and moves it from one end of the tape to the other.Īt one end of the bench is a device called a laser interferometer, which can precisely measure distances along the tape. Alongside the tape is a microscope, mounted on a moving carriage. They run the tape along a flat bench, holding it tightly in place with a specific tension from a mechanism or weight. Once the tapes are printed, manufacturers check random samples for accuracy. Some are printed using computer-controlled ink printers with tiny printheads to ensure the markings are laid down accurately. Some manufacturers use highly accurate reference tape measures to print their familiar hash marks on the tape. These length measurements and many others are often made with the help of a measuring tape. You need to measure length accurately to do things like make a dress, build a house, survey a plot of land, or determine if the home team made a first down on the football field.

Measuring tape use