• 1 mg to 30 kg weights.  Sold individually or as a weight sets.
• All weights meet or exceed ASTM specifications
• All mass measurements are made using procedures developed by NIST
• All mass standards are milled from the finest corrosion-resistant stainless steel stock ensuring consistent density
• Each weight is calibrated by a NVLAP-accredited metrology lab in a climate-controlled environment
• One-piece construction provides the maximum mass stability
• Each weight and weight set is supplied complete with a Certificate of Traceability
• Certificate of Calibration is available at an additional cost and must be ordered at time of placing order
• Each weight is calibrated by a NVLAP accredited metrology laboratory

Single-piece construction: Because the precise measurement of density can only be achieved using a single piece weight, all calibration weights are ASTM Type 1 single-piece weights.  These weights contain no air cavity or foreign adjusting material, thus providing the maximum mass stability.  In addition, it is an ASTM requirement that one-piece weights are used as standards and where mass stability is required.

A Choice of Preconfigured or Custom Weight Sets: Whether you choose a preconfigured weight set, or have a custom set made to meet your specific needs, be assured that all calibration weights are made of the highest quality materials.  Weight sets consist of flat weights in the 1mg to 500mg range and knob-style weights.

The mass standards produced today are designed to meet or exceed the standards of the American Society of Testing Materials (ASTM E617)

Which Class Calibration Weight is Right for My Application?
A balance should be calibrated using a weight with a class tolerance factor greater than the readability of the balance.  Example: A milligram balance with readability of 0.001g (i.e. A&D FX-300i - 320g x 0.001g) may be calibrated with a weight having a known tolerance of at least 0.0009g.

OIML E2 and Ultra Mass Class U Mass Standards.  These mass standards provide the greatest precision we offer.  They are ideal for use as reference standards to calibrate other weights or for calibrating high-resolution analytical balances.  Ultra Mass weights are identical to E2 weights except for the nominal value markings.  E2 weights have no markings on the weights, many customers prefer the weights be marked with the nominal value.  The OIML E2 tolerance is approximately two times the precision of ANSI/ASTM Class 1.

ANSI/ASTM Class 1 can be used as reference standard in calibrating other weights and appropriate for calibrating high-precision analytical balances (from 0.01mg to 0.1mg).

ANSI/ASTM Class 2 Appropriate for calibrating high-precision toploading balances with readabilities ranging from 0.001g to 0.01g.

ANSI/ASTM Class 3 Appropriate for calibrating balances with moderate precision, ranging from 0.01g to 0.1g.

ANSI/ASTM Class 4 Appropriate for student use and semi-analytical weighing.

NIST Class F Used to test commercial weighing devices by state and local weights and measures officials, device installers and service technicians. Class F weights may be used to test most accuracy class III scales, all scales of class III L or IIII, and scales not marked with a class designation.

Are all weights marked? YES

Small Knob weights marked with nominal values (100g,50g,20g......)

OIML shape marked with the nominal values (5,2,1,500,200,100,20,10..........) no gram designation

Do the calibration weights come with a specified due date for recalibration? NO

ISO/IEC 17025 paragraph 5.10.4.4 States: " A calibration certificate (or calibration label) shall not contain any recommendation on the calibration interval except where this has been agreed with the client.'  Therefore,we do not provide a calibration due date.  Setting calibration interval is the responsibility of the end user.  The certificate includes guidance information in the proper recertify cycle depending upon the use of the calibration weights.

Difference between Traceability and Cert of Calibration?

The major difference between the Report of Traceability and the Calibration Certificate is the Report of Traceability is a tolerance test and is only available for new weights.  The Certificate of Calibration is a full report of the parameters tested.  Below we outline what comes with each report.

Report of Traceability.
Each Ultra Mass , Class 1, Class 2 weight or weight set is supplied with a report of traceability at no additional cost.  This report identifies:

• Tolerance class
• Type of construction
• NIST test number
• Date of applicable primary standard(s)
• Secondary set number
• Includes technician's signature
• Description of the weight(s)
• Test Number
• Serial Number
• Nominal Value
• Uncertainty of the measurement tolerance
• Information on weighing procedures
• Date the primary standards were last tested at NIST and the NIST test number
• Date and test number for our working standards.
• Statement of compliance to ANSI/NCSL Z540 and ANSI/ISO/IEC 17025
• NVLAP Accreditation Logo and laboratory code.
• Statement of traceability to the International Prototype Kilogram (IPK) this meets the international requirement for traceability to the International System of Units.

Certificate of Calibration
Certificate of Calibration are available for any Ultra Mass, Class 1, or Class 2 weight or weight set.  The "W" at the end of the part number designates a Certificate of Calibration will be included with your weight(s).  The Certificate of Calibration includes everything found in a Report of Traceability listed above with the additional information listed below:

• 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 statistical 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.

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