What Does Legal-For-Trade Mean?

Legal-for-Trade scales are intended for commercial use applications. They are used when a product is sold by weight. Listed below are some examples where a Legal-for-Trade scale may be needed for commercial weighing:

  • Determination of mass for commercial transactions
  • Determination of mass for the calculation of a toll, tariff, tax, bonus, penalty, remuneration, indemnity or similar type of payment
  • Determination of mass for laws or regulations; expert opinion given in court proceedings
  • Determination of mass in the practice of medicine for the purposes of monitoring, diagnosis and medical treatment
  • Determination of mass for making up medicines on prescription in a pharmacy
  • Determination of mass in analyses carried out in medical and pharmaceutical laboratories
  • Determination of price based on mass for the purposes of direct sales to the public and the making-up of pre-packages

Commercial weighing and measuring equipment is defined as, “weights and measures and weighing and measuring devices commercially used or employed in establishing the size, quantity, extent, area, or measurement of quantities, things, produce, or articles for distribution or consumption, purchased, offered, or submitted for sale, hire, or award, or in computing any basic charge or payment for services rendered on the basis of weight or measure” according to NIST Handbook 44 and 130.

The National Conference on Weights and Measures (NCWM) and the Weights and Measure division of the National Institute for Standards and Technology (NIST) formed the National Type Evaluation Program (NTEP) that certifies Legal-for-Trade weighing equipment.

NTEP is a process that tests and evaluates weighing equipment to ensure compliance with NIST Handbook 44. If you’re considering a Legal-for-Trade scale, you will need to look for NTEP approval and a valid certificate of conformance number. GRM is a premier distributor for over 25 weighing and measuring equipment manufacturers. We professionally sell, calibrate and install legal-for-trade scales and balances. Contact us for further information!



Weighing Tips


Micrometer Calibration

Micrometers are used to measure thickness, diameters, and depth of slots with small distances. The rotations of the screw and thread forms are read from a scale and determine the accuracy. A micrometer is composed of a frame, anvil, barrel, lock nut, screw, spindle, thimble, and ratchet top. The frame is the thick C-shaped body that holds the anvil and barrel. The thickness minimizes contraction and expansion to maintain measurement accuracy. The sample rests against the anvil while the spindle moves towards it. The barrel is the stationary component with the scale on it. The lock nut is used to hold the spindle stationary. The screw is inside the barrel. The spindle is a cylindrical component that moves toward the sample and anvil. The thimble has graduated markings on it and is turned to move the spindle. Lastly the ratchet stop is at the end of the handle and limits applied pressure. 

When calibrating a micrometer, the standard accuracy must be greater than a 4:1 ratio over the accuracy of the gage being calibrated. The gage block must have a certificate of NIST traceability to have an accurate standard.

Here are some guidelines for a five-point calibration on micrometers:

  1. Look at the frame for any signs of damage
  2. Make sure the spindle and anvil faces are flat, free of pinholes, and are clean
  3. Check to see if the spindle feels smooth while moving the micrometer from 0 – 25ml. If it is hard to turn, there could be some damage. The micrometer should turn smoothly throughout the range
  4. Make any repairs that are needed to be done before proceeding
  5. Check five points with traceable gage blocks. For an example, you could take the entire range, split it in half, split it in half, split it in half again and split it for the last time. The zero point is repeatedly checked but not reported; and if you have a measurement point that is checked daily, then you should include that number in the calibration procedure.

To make sure your micrometers are calibrated accurately, you should have them done by an accredited calibration lab.


measurement with micrometers

calibrating micrometers

How to Properly Store and Handle Test Weights

Test weights are used to perform calibrations. It is very important to maintain their accuracy, and to do so there needs to be proper handling and storage of the test weights. If their accuracy is compromised, then calibrations will be off and product will be out of spec.


Class 1-7 test weights are held to the American Society for Testing and Materials (ASTM) standards and are most used in the laboratory.

These test weights should be kept in their original packaging. This with help keep dust and residue off the weights and keep them together. Store the weights near the balance to ensure they are controlled within the same temperature during use. An ideal temperature is 68 degrees Fahrenheit ± 2

When handling the test weights, be sure to use non-magnetic and non-abrasive tweezers. When possible, wear approved gloves. You should never use your bare hands to handle the test weights. The oils from your skin can affect the accuracy.


Class F test weights are held to NIST standards and are most often used in an industrial setting to calibrate larger scales.

These test weights aren’t required to be in as specific conditions as Class 1-7 test weights due to the tolerances involved. Just store these test weights in a clean dry environment and away from major contaminants.


Keeping your test weights under these conditions will save money because failure to do so results in re-calibration and decontamination of the test weights.

If you are in need of a calibration, we would be happy to assist you.




Calibration Weights

[Guide] Visual Scope of Services

With the largest scope of capabilities in the state of Michigan, Grand Rapids Metrology is a “one-stop shop” for calibration services. This document is a visual guide to all scale and metrology equipment Grand Rapids Metrology is NIST and A2LA accredited to service. Click to view our Visual Scope of Services.

Contact our experts to more information or quickly and easily request a quote today!

The Kilogram will be Redefined in 2018: Here’s What You Need to Know


“It’s not obvious that it’s a big deal, but it’s a big deal,” Chief of Quantum Measurement at the National Institute of Standards and Technology (NIST), Jon Pratt, said. His comment regarding a platinum and iridium cylinder that sits under lock and key in Serves, France. This cylinder is no ordinary mass, it’s THE kilogram, commonly referred to as “le grand k,” the weight that weighs exactly one kilogram, and the single standard by which all other kilogram’s are measured against. THE kilogram was crafted in 1889 as the golden standard for the weight and now resides at the International Bureau of Weights & Measure (BIPM).

The kilogram is the only SI unit defined by a manufactured object and as heavily revered as it is, there’s a problem. Scientist all over the world have recognized it. As a result, the kilogram is being redefined and we’ve got everything you need to about it.


NIST oversees weight and measurement standards in the United States and has spent the past few years diligently working in part with international effort to redefine “le grand k” based on a fundamental universal constant. They are seeking to use a physical quantity in nature, similar to the speed of light or electric charge of a proton, opposed to a manufactured mass of metal. A unit that never changes regardless of location or time. Essentially, changing this standard from an object to an idea.

But what’s wrong with the kilogram as is? Well, the standard kilogram at BIPM is losing weight as we speak. It was found to be lighter than it’s once identical “witnesses”, by the approximate weight of one eyelash.  The BIPM prototype may be losing mass due to the impurities in it’s metal or the witnesses are gaining mass by accumulating contaminants. Either way, this method of calibration has caused problems all around the world, but NIST’s solution could take this 19th century practice to a 21st or even 22nd century process.


After discovering the kilogram’s imperfections, the 2014 General Conference on Weights and Measures was held to discuss the redefining of the kilogram based on the Planck’s constant concept. This is a value from quantum mechanics that describes the packets energy comes in. The value of this constant was unknown during 2014 and no further decisions could be made regarding the kilogram. The team at NIST has since spent the past few years preparing for the 2018 General Conference by trying to find a number accurate enough to define Planck’s constant.

They have been using a Kibble balance, formerly known as a Watt balance, for this task. Instead of balancing scales with weights, the Kibble balance uses electromagnetism. If scientists know the current, velocity and voltage of the Kibble’s coil as it is pulled, the Planck constant can be determined with extreme precision.

After 16 months of work, NIST had finally announced their findings. Planck’s constant was 6.626069934 x 10−34 kg∙m2/s with an uncertainty of 0.0000013%. In 2018, the next General Conference on Weights and Measure will take place where the scientific community will draft a resolution to redefine the kilogram based on this new found constant.


The bottom line is that this massive and innovative discovery won’t affect you much at all. Your scales and metrology equipment will continue to be calibrated by Grand Rapids Metrology’s set of standards which are calibrated by the State of Michigan which are calibrated by NIST and A2LA standards which are calibrated by the kilogram at BIPM in France. The only aspect of that equation that will change 2018 and beyond is the kilogram will transform from a physical object to an very precise idea.

This modernization will prevent any error in the standard of the kilogram. Deteriorating metal or added contaminants will no longer be a problem. Rest assured your equipment will remain calibrated to the highest standards and your piece of mind will stay intact during this transition.

For even more about the redefining of the kilogram, check out this article from NIST’s website.

Reference: The Washington Post: Speaking of Science

The Difference Between A2LA and NIST

As you know, Grand Rapids Metrology is A2LA accredited to ISO 17025 standards in numerous measurement calibrations such as temperature, humidity, mechanical metrology, dimensional metrology, and much more. In previous blog posts, we have discussed the basics of A2LA and why it is so important to us and to our customers. Likewise, we have discussed NIST and NIST traceable calibrations but never have we pinned these two organizations in the ring against one another. There’s a first time for everything, so here we go.

A2LA is an acronym for the American Associations for Laboratory Accreditation and it is a non-profit, non-governmental, third-party, public service, accreditation body. NIST, on the other hand, stands for National Institute of Standards and Technology and is a measurement agency that is a part of the U.S. Department of Commerce, also one of the nation’s oldest physical science laboratories. For any organization using an instrument that requires calibration, it is vastly important to understand the distinction between a NIST traceable calibration and an A2LA accredited calibration.

Being NIST traceable simply means that the equipment being used to calibrate customer’s equipment is traceable to NIST standards, but an A2LA accreditation means a bit more. A2LA is, as stated before, an accreditation body that accredits outside laboratories to numerous standards, specifically ISO 17020, 17043, 17065, and 17025. Grand Rapids Metrology is accredited by A2LA to ISO 17025 standards which means not only is GRM’s equipment NIST traceable, but also the methods we use comply with ISO 17025 standards. Thus, an A2LA accreditation is always NIST traceable, but NIST traceable calibrations are not always A2LA certified calibrations.

At this point, it may seem that A2LA has the upper hand on NIST, however these organizations do not perform or provide the exact same services; therefore, we must acknowledge their attributes individually. It is important to note that NIST equipment are traceable through a chain of preceding standards that ultimately lead to the original calibration, or the “gold standard.” The closer your standards are to the gold standard, the more accurate the calibration and vice versa. Likewise, NIST is only able to certify certain classes of weights the farther away from the gold standard the piece of equipment is, often the class options become fewer as the chain continues. Contrariwise, A2LA offers programs for the accreditation services and training for virtually any industry. After the accreditation certification has been approved, the organization is able to operate freely with these certifications during the time they are valid.

At the end of the day, measurement standards are essential to the constant flow and operation of our society. Having NIST traceable equipment makes for a positive attribute to your organization, however being accredited by A2LA is taking an extra step. Ultimately, A2LA allows for more precise measurements and calibration. GRM is proud to be A2LA in every aspect of our scope with the exception of electronic equipment, but not for long (our electronic accreditations will be here Fall 2016)!