# How To Determine a Kilogram **URL:** \ **Category:** Factual Questions\ **Created:** [June 30, 2016, 9:17pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828 "2016-06-30T21:17:59Z")\ **Posts on this page:** 20\ **Page:** 4
**Author:** ![nate](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nate/32/13085_2.png) [@nate](https://boards.straightdope.com/u/nate)\ **Post date:** [July 6, 2016, 2:55pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/61 "2016-07-06T14:55:22Z")
> [@Blue\_Blistering\_Barnacle](#): > > I guess in a pinch, it could define its own local kilogram standard (based on a volume of liquid, or something), which may be good enough. No doubt it would be good enough. If it needed a mass standard, any stable mass would do. The challenge is being able to measure like masses so that copies this machine creates can verify the “exactness” of its copies. The tolerances for how well the copy needs to be like the original would determine how good the measurement needs to be. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [July 6, 2016, 3:28pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/62 "2016-07-06T15:28:33Z")
> [@Leo\_Bloom](#): > > How do the professional societies–the Institute of Electrical and Electronics Engineers (IEEE), American Society of Mechanical Engineers, eg–interact with these specifying chains as to their own standards? > > > [@Crafter\_Man](#): > > > > No one needs to interact. > > > > Is your instrument calibrated and traceable to NIST? _Is the uncertainty of the instrument known and properly determined?_ If you answer “yes” to both, then you’re good to go, regardless of what anyone else is doing. [italics added] > > > > > [@Leo\_Bloom](#): > > > > > > **Crafter\_Man** , thanks. It occurred to me after I posted that it was a stupid question–IEEE says “not to exceed 3 volts, and we mean 3 volts. Up to you to prove it.” … Well, my opinion of the question needs to be revised, and in a way the “interaction” is profound: … The American Society of Mechanical Engineers (ASME) has produced a suite of standards addressing various aspects of measurement uncertainty. ASME B89.7.3.1, Guidelines for Decision Rules in Determining Conformance to Specifications addresses the role of measurement uncertainty when accepting or rejecting products based on a measurement result and a product specification. ASME B89.7.3.2, Guidelines for the Evaluation of Dimensional Measurement Uncertainty, provides a simplified approach (relative to the GUM) to the evaluation of dimensional measurement uncertainty. ASME B89.7.3.3, Guidelines for Assessing the Reliability of Dimensional Measurement Uncertainty Statements, examines how to resolve disagreements over the magnitude of the measurement uncertainty statement. ASME B89.7.4, Measurement Uncertainty and Conformance Testing: Risk Analysis, provides guidance on the risks involved in any product acceptance/rejection decision. The “Guide to the Expression of Uncertainty in Measurement”, commonly known as the GUM, is the definitive document on this subject. The GUM has been adopted by all major National Measurement Institutes (NMIs), by international laboratory accreditation standards such as ISO/IEC 17025 General requirements for the competence of testing and calibration laboratories which is required for international laboratory Accreditation, and employed in most modern national and international documentary standards on measurement methods and technology… Wiki “Measurement uncertainty”:[Measurement uncertainty - Wikipedia](https://en.m.wikipedia.org/wiki/Measurement_uncertainty) ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [July 6, 2016, 3:39pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/63 "2016-07-06T15:39:50Z")
Is it interesting to anyone besides me that the measurement uncertainty standards cited above are given their imprimatur by (nominal) Mechanical Engineers, and not the American Physical Society, or some such? Something reassuring and grounded in that. ---
**Author:** ![nate](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nate/32/13085_2.png) [@nate](https://boards.straightdope.com/u/nate)\ **Post date:** [July 6, 2016, 4:11pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/64 "2016-07-06T16:11:10Z")
> [@Leo\_Bloom](#): > > Is it interesting to anyone besides me that the measurement uncertainty standards cited above are given their imprimatur by (nominal) Mechanical Engineers, and not the American Physical Society, or some such? > > Something reassuring and grounded in that. To me it seems as though the ASME has published a guide interpreting the GUM for use in mechanical engineering fields. Not counting the numerous real-world examples found in the document, the GUM is very general and brief. It doesn’t surprise me that an organization would produce a guide derived from the GUM for specific applications. The GUM itself is a creation from a working group with representatives from each of the following: International Bureau of Weights and Measures (BIPM) International Electrotechnical Commission (IEC) International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) International Organization for Standardization (ISO) International Union of Pure and Applied Chemistry (IUPAC) International Union of Pure and Applied Physics (IUPAP) International Organization of Legal Metrology (OIML) International Laboratory Accreditation Cooperation (ILAC) ---
**Author:** ![leahcim](https://avatars.discourse-cdn.com/v4/letter/l/b4bc9f/32.png) [@leahcim](https://boards.straightdope.com/u/leahcim)\ **Post date:** [July 6, 2016, 4:24pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/65 "2016-07-06T16:24:41Z")
> [@Blue\_Blistering\_Barnacle](#): > > I guess in a pinch, it could define its own local kilogram standard (based on a volume of liquid, or something), which may be good enough. And 100000 years later some of the Von Neumann probes circle back to their original launch point, only to discover that they are 1/10th the size of the original. ---
**Author:** ![RadicalPi](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/radicalpi/32/9806_2.png) [@RadicalPi](https://boards.straightdope.com/u/RadicalPi)\ **Post date:** [July 6, 2016, 4:44pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/66 "2016-07-06T16:44:30Z")
> [@Crafter\_Man](#): > > Today the meter is defined as “1,650,763.73 wavelengths of the orange-red emission line in the electromagnetic spectrum of the krypton-86 atom in a vacuum” ([link](https://en.wikipedia.org/wiki/Metre#Number_of_wavelengths_of_red-orange_emission_line_of_krypton-86)). That’s an older standard. Today, the meter is defined as 1/299,792,458 of the distance light travels (in a vacuum) in one second. ---
**Author:** ![MaxTheVool](https://avatars.discourse-cdn.com/v4/letter/m/9fc29f/32.png) [@MaxTheVool](https://boards.straightdope.com/u/MaxTheVool)\ **Post date:** [July 6, 2016, 4:48pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/67 "2016-07-06T16:48:44Z")
> [@RadicalPi](#): > > That’s an older standard. Today, the meter is defined as 1/299,792,458 of the distance light travels (in a vacuum) in one second. Crafter Man just got metrology BURNED!!! ---
**Author:** ![Blue\_Blistering\_Barnacle](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/blue_blistering_barnacle/32/3386_2.png) [@Blue\_Blistering\_Barnacle](https://boards.straightdope.com/u/Blue_Blistering_Barnacle)\ **Post date:** [July 6, 2016, 4:53pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/68 "2016-07-06T16:53:13Z")
> [@leahcim](#): > > And 100000 years later some of the Von Neumann probes circle back to their original launch point, only to discover that they are 1/10th the size of the original. Sounds 'Hitch-hiker’s Guide"-ish. "The entire fleet was swallowed by a small dog. " ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [July 6, 2016, 5:54pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/69 "2016-07-06T17:54:38Z")
> [@nate](#): > > To me it seems as though the ASME has published a guide interpreting the GUM for use in mechanical engineering fields. Not counting the numerous real-world examples found in the document, the GUM is very general and brief. It doesn’t surprise me that an organization would produce a guide derived from the GUM for specific applications. > > The GUM itself is a creation from a working group with representatives from each of the following: > > International Bureau of Weights and Measures (BIPM) > International Electrotechnical Commission (IEC) > International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) > International Organization for Standardization (ISO) > International Union of Pure and Applied Chemistry (IUPAC) > International Union of Pure and Applied Physics (IUPAP) > International Organization of Legal Metrology (OIML) > International Laboratory Accreditation Cooperation (ILAC) Ahh…there go those other guys. Guess I should have known they’d be around somewhere… Thanks. Example of what happens when one overzealous Wiki contributor hijacks the balance of the entry, leading to guys like me grasping the wrong end of the stick. (But it is nice to remember these cockamamie things have to get _built_ eventually. Go ASME!) [I am an ex-employee.] ---
**Author:** ![PastTense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pasttense/32/14550_2.png) [@PastTense](https://boards.straightdope.com/u/PastTense)\ **Post date:** [November 3, 2018, 5:25pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/70 "2018-11-03T17:25:55Z")
Updating this thread the exciting event is going to happen this month! > [@](#): > > On 16 November 2018 metrologists and policy-makers from 60 countries around the world will gather at the General Conference on Weights and Measures (CGPM) in Versailles, France. Nothing unusual there, as the meeting convenes once every four years to discuss budgets and issues in metrology. But this meeting will be special. Member states will be voting on whether to adopt the most sweeping change to the International System of Units (Système International, or SI) since its inception in 1960. It is a change that will include new definitions of the kelvin, ampere and mole, but perhaps most significantly the kilogram. > > Each member state will cast its one vote in a process that will be streamed live online. If the change is ratified (and all the signs are that it will be) the event will mark the end of basing units on objects – a practice dating back millennia. It will also finally fulfil a wish first voiced by James Clerk Maxwell, who predicted that measurement standards might somehow be defined by immutable constants of nature. > **[SI gets a makeover – Physics World](https://physicsworld.com/a/si-gets-a-makeover/)** > > A key meeting this month is likely to see all SI units defined for the first time in terms of fundamental constants. Benjamin Skuse explains the change Another explanatory article: > **[The future of the kilo: a weighty matter](https://www.theguardian.com/science/2018/nov/03/the-future-of-the-kilo-a-weighty-matter-international-prototyp-kilogram-paris-kibble-balance)** > > A lump of metal in a building near Paris has long served as the global standard for the kilogram. That’s about to change… ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [November 3, 2018, 5:33pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/71 "2018-11-03T17:33:03Z")
Surprised this hasn’t been posted yet. Here is a great video describing this whole thing: [Veritasium - The World’s Roundest Object](https://www.youtube.com/watch?v=ZMByI4s-D-Y) ---
**Author:** ![Ranger\_Jeff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ranger_jeff/32/2065_2.png) [@Ranger\_Jeff](https://boards.straightdope.com/u/Ranger_Jeff)\ **Post date:** [November 3, 2018, 9:42pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/72 "2018-11-03T21:42:06Z")
Just for the record, the formal definition of a second in the International System of Units (SI) is defined to be exactly 9,192,631,770 cycles of a Cesium atomic clock. When I was in the USCG, I was responsible for the care and feeding of 3 of them. The 5 Mhz, 1 Mhz, and 100Mhz outputs were no problem. The challenge was to set the one pulse per second output. The second was broadcast from Fort Collins. I had to account for the 8.7 msecs it took took the beep to travel from Ft. Collins to NYC. When your plus or minus is in femtoseconds, you do what you can. ---
**Author:** ![mikecurtis](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mikecurtis/32/3284_2.png) [@mikecurtis](https://boards.straightdope.com/u/mikecurtis)\ **Post date:** [November 3, 2018, 9:50pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/73 "2018-11-03T21:50:08Z")
> [@Whack-a-Mole](#): > > Surprised this hasn’t been posted yet. Here is a great video describing this whole thing: [Veritasium - The World’s Roundest Object](https://www.youtube.com/watch?v=ZMByI4s-D-Y) I did in a different thread > [@Is there a standard for temperature similar to those for length, mass, etc.?](https://boards.straightdope.com/t/is-there-a-standard-for-temperature-similar-to-those-for-length-mass-etc/814585/48): > > here’s an [interesting video](https://www.youtube.com/watch?v=ZMByI4s-D-Y) on trying to change the definition on a kilogram, so it no longer relies on the vagaries of a physical object. ---
**Author:** ![whitetho](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whitetho/32/1059_2.png) [@whitetho](https://boards.straightdope.com/u/whitetho)\ **Post date:** [November 3, 2018, 10:31pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/74 "2018-11-03T22:31:56Z")
> [@Doughbag](#): > > Don’t confuse the issue with using kg and lb… If your earth weight is 90kg, you would weight 14.9kg on the moon. [Cite](http://www.exploratorium.edu/ronh/weight/) Technically, using metric (SI) units, shouldn’t this read “your mass on both Earth and the moon is 90kg, while your weight on earth is approx. 883 Newtons (90\*9.80665) and on the moon is about 1/6th of that, or 147 Newtons”. (“Newtons” is the metric unit for force if I understand these things correctly). ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [November 3, 2018, 10:39pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/75 "2018-11-03T22:39:18Z")
The round sphere isn’t being used for the new KG, this was the International Avogadro Project and was rejected this idea and went with the Planck constant. The mole is what is being defined with those spheres. The kilogram, ampere, kelvin and mole are all being changed. Here is a link to a good overview showing what the expected changes. [http://www.npl.co.uk/si-units/redefining-the-si-units/](http://www.npl.co.uk/si-units/redefining-the-si-units/) ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [November 3, 2018, 10:50pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/76 "2018-11-03T22:50:05Z")
It does look like veritasium does have a video that explains the Kibble ballance. [![](https://img.youtube.com/vi/Oo0jm1PPRuo/maxresdefault.jpg "How We're Redefining the kg") ](https://www.youtube.com/watch?v=Oo0jm1PPRuo) ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [November 3, 2018, 11:11pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/77 "2018-11-03T23:11:29Z")
> [@Chronos](#): > > Yes, there are units of mass and force which are both called “pound”. They are two completely different units, and cannot be compared. And it was idiotic to set up a system (or mishmash of systems) where two different units could be assigned the same name like that. In fact, one might even say that those who set up that mishmash of systems did it wrong. The person who is responsible for this mishmash of units deserves a good slug, followed by a pounding… ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [November 4, 2018, 12:03am UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/78 "2018-11-04T00:03:43Z")
> [@Andy\_L](#): > > The person who is responsible for this mishmash of units deserves a good slug, followed by a pounding… While it is frustrating really it is due to different needs wanting the simplest formulas for their uses more than anything else. Really the bias can be illustrated by the form of Newtons 2nd law of motion. If you prefer F=ma you will have kilograms and newtons/pounds and slugs but some applications prefer m = F/a which ends up with kilograms and kilograms-force (kilopond)/pounds and pounds-force. The kilopond was used in Germany until the late 1970’s. In the US the FPS system is still in use by Engineers and has the pound-force base unit that actually causes the problems with the slug. While not arguing the benefits or values, the official NIST pound has been a unit of mass forever and has been defined off the kilogram for just about as long as there was a kilogram. Funny enough, with the new method the Kilogram is now derived in part by _weighing_ an object as a part of the process. It doesn’t matter much unless one wants to use the “operational” definition of weight as until GR is disproved (not just found incomplete) internal mass and weight are just two methods to measure the same fundamental property. Einstein’s paper on General Relativity has this postulate, which is why I make this claim. > [@](#): > > A satisfactory interpretation can be obtained only if we recognise the following fact : The same quality of a body manifests itself according to circumstances as " inertia " or as " weight " (lit. " heaviness '). Not that it will change needs or limitations of coherent systems, but as the original kilogram was the kilopond or kilogram-weight and the kilogram-mass was changed to be _the_ kilogram it is funny that in one line of thinking the definition kind-of took a round trip. With the new balance method the basic equivalence in the Kibble Balance is. mg = IBL Where: m = mass; g = gravity; I = current; B = magnetic field strength; L = length of wire As obviously “mg” is the force/weight, it will be interesting to see how the confusion develops over time. It would be really nice if Engineers would quite using the slug base unit as while that wouldn’t be as convenient as switching to SI for conversion at least everything would be defined off the same base units and coherent system. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [November 4, 2018, 12:56am UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/79 "2018-11-04T00:56:46Z")
> [@mikecurtis](#): > > I did in a different thread Cool. It seems he did another, more recent, video on the [Watt Balance](https://www.youtube.com/watch?v=Oo0jm1PPRuo) approach to defining the kilogram (which he briefly mentions in the sphere video). It seems a damn-sight more complex than the sphere approach but supposedly these are complementary approaches and can be used to be a check on each other. The science of this one is hard to follow though as it seems a bit convoluted (which is not to say needlessly so or not good…just it has a lot of steps to get to where they are going). Still pretty cool and it is amazing the precision scientists can manage today. EDIT: Looks like rat avatar beat me to this video. ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [November 4, 2018, 1:07am UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/80 "2018-11-04T01:07:59Z")
> [@whitetho](#): > > Technically, using metric (SI) units, shouldn’t this read “your mass on both Earth and the moon is 90kg, while your weight on earth is approx. 883 Newtons (90\*9.80665) and on the moon is about 1/6th of that, or 147 Newtons”. (“Newtons” is the metric unit for force if I understand these things correctly). To clarify, Mass is actually not the amount of matter contained by a body a Mole is. Mass (in general and in classic physics) is a measure of a body’s resistance to acceleration. The acceleration due to gravity is also not consistent on the surface of earth, but we typically don’t need to weigh things with enough precision to worry about that in a typical persons life. In science the _weight_ of a body in a particular reference frame is defined as the force that gives the body an acceleration equal to the local acceleration of free fall in that reference frame (ISO 80000-4). In every day usage the verb “to weigh” means “to determine the mass of” or “to have a mass of.” Under the scientific use there is actually no reason to use the term “weight” in either case and they can be called out as force or as just “mass” now that the terms atomic weight and molecular weight are obsolete. The _newton_ is useful as a unit of force when you need to reference a “force” If you have a bathroom scale that is calibrated to _the standard value for the acceleration of gravity_ or 9.806 65 m/s2 exactly; and your local gravity on earth is not significantly different from that number that was based on at a random spot in France at 45 degrees latitude your scale will be accurate. If your local gravity differs significantly from the standard value of the acceleration due to gravity, g\_n = 9.806 65 m/s2 exactly; you will need to correct your measuring devices for the local acceleration of gravity to detect the “mass” of an object. The fact that it deviates **more** from the standard value of the acceleration due to gravity on the moon just means that the error rate is too much to use in that convenient form if you are looking for a general estimation of the mass of an object. If you are trying to check floor loading or how much rocket propellant you need, the _force_ or newtons is a better unit of measure. The simple answer is to use the units that you are trying to solve for. Use newtons to solve: force = acceleration \* mass Use kilograms to solve: mass = force / acceleration The units are driven by the answer you are looking for, not the mistaken basic physics description that over-complicates the issue while also ignoring the assumption of a known value for acceleration. It is a good example on how math is a lot simpler for these concepts. The critical thing to understand is that both the force from gravity and the mass are due to the same fundamental underlying property of an object. [Previous page](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828.md?page=3) [Next page](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828.md?page=5)