• Uncertainty value
• Test conditions temperature, barometric pressure, humidity.
• Conventional Mass Correction
• Uncertainty of the measurement
• Identification of the balance used in the calibration
• as found value if an adjustment is performed
• assumed density of the weight
• material weight is made from
• Pass/Fail result of magnetic testing
• Volume of the weight
• Cubical Coefficient of expansion
• True Mass correction

Who do you feel needs a Calibration Certificate verses Report of Traceability?

If you are under ISO, FDA or other regulation they should get a Calibration Certificate.  Also, anyone that plans to calculate uncertainty for their own process would need the certificate of calibration so they could correctly include our uncertainty into their own uncertainty budget.

If they have a balance or scale with the ability to read to a milligram or better it is always recommend they know the corrected value of the weight and this is only available with the Calibration Certificate.

Recertification Service
Weight values can change over time due to scratches, fingerprints, wear and even corrosion resulting from atmospheric contaminants.  Regular checks on the accuracy of mass standards ensures the accuracy of measurements.  We have access to mass metrology lab providing this service at a very competitive prices. 

The rates vary depending upon the size of the weight (1 gram cost less than a 5kg weight) are listed below and subject to change.  Typical turn around time (excludes transit time) is 7 to 10 business days upon receipt at the metrology lab.  You are responsible for both in and out bound freight and insurance costs.

• Single weights - 1g - $44 , 5kg - $144
• Weight sets depend upon the amount of weights in a set - 21 piece set 1mg - 100g - $854

Please call us for up to date pricing and the procedure involved in sending your weights in for recertification.

What does calibration of a laboratory weight entail?

All calibrations are accredited calibrations performed using weights by NIST weighing designs, where all weights are compared against 2 standards.  The mass comparators used for performing the calibration ascertain and measure differences to 10, 1, and even 0.1 micrograms (one ten-millionth of a gram).  The value of the unknown weight is computed using a least sum squares technique by the NIST masscode software.  The software performs stastical checks on the balance performance and the computed values of the second standard.  If the balance performance or computed value of the second standard are found to be unacceptable the software requires that the measurement be repeated.  It is only when the process standard deviation and computed value of the check standard are acceptable that metrologist is confident in the value for the customer's weight.  All measurements in metrology laboratory, including tolerance testing, use this Echelon I weighing technique.  The weighing designs are the same ones developed and used by NIST.  All measurement results are traceable to the International Prototype Kilogram (IPK) through a NIST calibration of our primary standards.

Calibration technicians must wear appropriate static free clothing, as well as gloves, hair nets and face masks, to reduce the possibility of contamination (and changing the weight of the weights) from skin oils, hairs, or airborne droplets.  Calibration weights are never touched directly by human hands.

What is True Mass Correction?

Basically, the only people who use "True Mass" are calibration laboratories and other people who apply air buoyancy corrections to the measurements.  Conventional mass is what a weight would weigh at sea level at standard temperature and pressure.  Since most people use their weights in air and don't have the equipment or desire to measure and calculate the air density they have no need for the true mass values.  NVLAP published NIST Handbook 150-2G requiring calibration certificates to reporting "true mass".  If someone needs true mass they typically will know how to calculate it from the Conventional mass.

What is Uncertainty?

Uncertainty is more than just the repeatability of the balance it is a summation of all things which contribute to the error in the measurement process.  Uncertainty is the root sum square of balance deviation, repeatability on the check standard, variability in the density of the standard, variability in the density of the weight under test, variability of the temperature, variability of the barometric pressure, variability of the humidity, operator skill and the uncertainty of the standard used multiplied by two.

What is the difference in tolerance between Ultra, Class 1, Class 2 and other calibration specifications?

Metric Weight Tolerances - all tolerances stated in milligram (mg)
	American Society of Testing & Measurement ASTM E617									International Organization of Legal Metrology Recommendation R111
Denomi- nation Metric	Ultra Class	Class 1 mg	Class 2 mg	Class 3 mg	Class 4 mg	Class 5 mg	Class 6 mg	Class 7 mg		E1 mg	E2 mg	F1 mg	F2 mg	M1 mg	M2 mg	M3 mg
5 kg	6.00	12	25	50	100	250	500	1400		2.5	7.5	25	75	250	750	2500
3 kg	3.80	7.5	15	30	60	150	300	1000
2 kg	2.50	5.0	10	20	40	100	200	750		1.0	3.0	10	30	100	300	1000
1 kg	1.25	2.5	5.0	10	20	50	100	470		0.5	1.5	5	15	50	150	500
500 g	0.600	1.2	2.5	5.0	10	30	50	300		0.25	0.75	2.5	7.5	25	75	250
300 g	0.380	0.75	1.5	3.0	6.0	20	30	210
200 g	0.250	0.50	1.0	2.0	4.0	15	20	160		0.1	0.30	1.0	3.0	10	30	100
100 g	0.125	0.25	0.50	1.0	2.0	9	10	100		0.05	0.15	0.5	1.5	5	15	50
50 g	0.060	0.12	0.25	0.60	1.2	5.6	7			0.030	0.10	0.30	1.0	3.0	10	30
30 g	0.037	0.074	0.15	0.45	0.90	4.0	5	44
20 g	0.037	0.074	0.10	0.35	0.70	3.0	3	33		0.025	0.080	0.25	0.8	2.5	8	25
10 g	0025	0.050	0.074	0.25	0.50	2.0	2	21		0.020	0.060	0.20	0.6	2	6	20
5 g	0.017	0.034	0.054	0.18	0.36	1.3	2	13		0.015	0.050	0.15	0.5	1.5	5	15
3g	0.017	0.034	0.054	0.15	0.30	0.95	2	9.4
2 g	0.017	0.034	0.054	0.13	0.26	0.75	2	7.0		0.012	0.040	0.12	0.4	1.2	4	12
1 g	0.017	0.034	0.054	0.10	0.20	0.50	2	4.5		0.010	0.030	0.10	0.3	1.0	3	10
500 mg	0.005	0.010	0.025	0.080	0.16	0.38	1	3.0		0.008	0.025	0.08	0.25	0.80	2.5
200 mg	0.005	0.010	0.025	0.060	0.12	0.26	1	1.8		0.006	0.020	0.06	0.20	0.6	2
100 mg	0.005	0.010	0.025	0.050	0.10	0.20	1	1.2		0.005	0.015	0.05	0.15	0.5	1.5
50 mg	0.005	0.010	0.014	0.042	0.085	0.16	0.5	0.88		0.004	0.012	0.04	0.12	0.4
20 mg	0.005	0.010	0.014	0.035	0.070	0.12	0.5	0.56		0.003	0.010	0.03	0.10	0.30
10 mg	0.005	0.010	0.014	0.030	0.060	0.10	0.5	0.4		0.002	0.008	0.025	0.08	0.25
5 mg	0.005	0.010	0.014	0.028	0.055	0.080	0.2			0.002	0.006	0.020	0.06	0.20
2 mg	0.005	0.010	0.014	0.025	0.050	0.060	0.2			0.002	0.006	0.020	0.06	0.20
1 mg	0.005	0.010	0.014	0.025	0.050	0.050	0.1			0.002	0.006	0.020	0.06	0.20
The table above is a listing of the tolerances of various classes of masses.  The weight value can deviate above or below the nominal value by the tolerance defined.  To determine the tolerance of a mass, look at the denomination or nominal value of the weight and the appropriate class you need.
Custom weight sets are available upon request by calling Precision Weighing Balances at 978-521-7095
All calibration weights are not returnable.  Once your order has been placed it CAN NOT be cancelled.  Please carefully consider this prior to placing your order.  The reason for this is these weights are custom manufactured and are certified on the date they were made.  In addition, if you touch the calibration weight with your fingers the oil in your skin would change the tolerance and we can not take this chance if the weight was returned.