Why Use Standard Units?
Date: August 2006
Why is it important to use standard units (SI) when
doing a scientific inquiry?
I do not think that the choice of units necessarily affects the
quality of a scientific inquiry. How good or how scientific the
inquiry can be depends on the kinds of questions that are asked, the
methods chosen, the design of the experiment, how well the
parameters are defined.
However, there are advantages to using SI units. For one thing SI
units are in base 10, they go in decimal ranges and converting to
bigger or smaller units of measure is just a matter moving the
decimal place or changing the factor of 10. It is also easier to
remember the relationship between units, I still have to stop and
think whenever I try to remember how many pints are there in a
gallon or how many feet to a mile. That does not happen when I try
to convert meters to kilometers or milliliters to liters.
When we have the data or results of our inquiry, we do have to
communicate that efficiently. Agreeing to use SI units (which has
the above mentioned advantages) makes for a more efficient communication.
Greg (Roberto Gregorius)
Physical quantities have "units" feet, grams, seconds, and so on. It
is important to the communication of knowledge that scientists (and
others) make sure that the numbers being communicated are in the
same units for obvious reasons. If you are talking about 60 seconds
and I am talking about 60 hours it makes much difference. As
scientific study has progressed scientists have been concerned with
using the most meaningful, fewest and most fundamental groups of
units. This process is on-going all the time. In the United States,
the National Institute of Science and Technology (NIST) has the
responsibility of continually researching current standards and
researching how to improve their measurement and consistency. You
can find the NIST web sites that have to do with these standards at
There are many interesting stories on the various links.
It is very important to use a standard set of units and there are a
couple of good reasons. Think of a large group of people trying to work
together to solve a problem or build something, but doing so in many
If everyone uses the same system of units, then there is less likelihood
of mistakes. Most of the time a mistake in the units (or conversion
from one set to another) is easy to catch. Regrettably however, it does
happen. One of the most infamous cases of this in recent history was
the loss of NASA's Mars Climate Observer spacecraft. The probe had a
fatal mistake buried deep inside that no one figured out (until it was
too late). Engineers from Lockheed calculated a series of data used to
control how the spacecraft was maneuvered. Lockheed did the calculation
in English units (pounds) and NASA used the data as though it was
calculated in SI units (Newtons). That single factor brought down a 125
million dollar spacecraft.
Secondly, it is just easier to communicate and get your ideas across. If
a researcher writes a paper using a poor choice of units (especially an
experimental scientist), the results can be clouded or obscured. While
it is true enough that (assuming everything was done correctly) anyone
else could sit down and convert the units into something easily
understandable, very often that simply will not happen. If someone does
an interesting experiment or finds an interesting result, other people
simply may not recognize it as such if it's not presented in a way that
is easy to grasp.
There are also more subtle reasons too. For instance, it is best to
units that are appropriately chosen for the system you are studying. It
makes little sense to measure the mass of a mountain in atomic mass
units and measuring the mass of a single atom in kilo-grams isn't too
great of an idea either. There are also units which came about through
a historical reason. Those units may have been ok at the time, but as
the system is better understood it may become apparent that there is a
Simply put, If you have got a large number of people working together,
it is best if they can fluently speak a common language. That is
basically why scientists the world over try to use a singular set of
units. Or at least it is why I wish we all used a single set of units!
Michael S. Pierce
Materials Science Division
Argonne National Laboratory
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Update: June 2012