Hi,
I wonder if there is a way to tell smath to use electrical units as default. Eg. it gives me results of Ohms in (kg*m2)/(A2s3). I know I can set manually units but is so annoying doing it again and again when you focus on electrical units.

Regards
Kriss

Wrote

Hi,
I wonder if there is a way to tell smath to use electrical units as default. Eg. it gives me results of Ohms in (kg*m2)/(A2s3). I know I can set manually units but is so annoying doing it again and again when you focus on electrical units.

In short: the pure physical SI unit system is useless [mostly]
for Engineering projects. An acceptable option would be the
unit system as pure decoration and carried as such or like
many of the users => totally unitless, append UnitResult.

Cheers.

I get Ohms as default. Can you attach an example?

Best regards.
Alvaro.

Wrote

In short: the pure physical SI unit system is useless [mostly]
for Engineering projects.

Make a search in the forum to find out where 90% of statements qualifying other peoples's stuff as "useless" come. In 90% of these cases "useless" is used as synonym for "I don't like it" or "I don't understand it" which would be much less insulting. And in quite some fraction of the cases this is not driven by the desire to help with the original post but just to vote for something.

Helping SMath users with unit problems by telling them not to use SMath's unit features is like telling a Word user with spelling problems not to use the keyboard.

You have a good point Martin,

My point is that for Engineering works, one must be able to use books and standards as they existed
and still exist to produce result. As an example, BIPM use Ohm for the Pt resistance thermometer.
IAPWS lists the units [about 3/4 page] and you just plug what you measure physically or plug one
to retrieve all the dependents. In over 125000 messages Mathsoft Collaboratory, not a single one
carried units [I read all of them, contributed to > 25000]. Units were discussed ad nauseum, not
enough to convince users. Why should a result not return m/s from a formula ...
More recently, collab entered Ohm and didn't get Ohm result.
Most annoying is "units don't match", then zap units ... pre-define what they are up top WS.
Arc length is from unitless formulas, result is "GraphUnit" that you can post define is anything
that belongs to the project [m, km, year-light ...].
Using WASP from Katmar, I plug 200 °C and get speed of sound in m/s, not Gy/K like recently.
Years ago, when I started Consulting, my TI-48 had no unit system, no plant exploded from formulas
heritage over decades.
In Engineering we use mostly "derived units" for which strictly SI is not compatible.
As long as Smath can do my projects unitless, fine.

Process Engineers never insulted me giving the massflow rate in T/hr to calculate the orifice bore Diameter,
and that is fully compatible to the standard ISO-5167... few steps TI-48 ...
More comfortable in Mathcad, Smath ... and documented rather than hand writing.

Цитата

In Engineering we use mostly "derived units" for which strictly SI is not compatible.

Please give an example of such non-compatibility.

Wrote

Please give an example of such non-compatibility.

{'kg*'m^2}/{'A*'s^3} instead of V [Volt] ... few days ago.

BJT Circuit Analysis (1) (1).sm (90 КиБ) скачан 38 раз(а).

A multi-meter reads V, even better: reads DC/AC and Ω

Those are not incompatible though.



You can perform operations between the two.

Цитата

Most annoying is "units don't match", then zap units

When you get this error, it means you are trying to perform an operation between units that is not compatible. Like adding volts and amps together.
In my opinion, that's one of the biggest benefits of using units in calculation. You can immediately get an idea if you're equations produce an accurate result.
Even if the default units are not necessarily in the format you're use to seeing, you can easily change that unit to see if it's compatible.

Wrote

Wrote

Please give an example of such non-compatibility.

{'kg*'m^2}/{'A*'s^3} instead of V [Volt] ... few days ago.

BJT Circuit Analysis (1) (1).sm (90 КиБ) скачан 38 раз(а).

A multi-meter reads V, even better: reads DC/AC and Ω

Your statement was on the SI-System, not on SMath. Your example isn't related to SI. It is just SMath behaviour. It would help to cleanly distinguish concepts and their possibly non-perfect implementation.

I don't know if there are other common/sensible interpretations of {'kg*'m^2}/{'A*'s^3} than V. If not, then SMath should be able to use this shortcut. However, keeping base units is safe, whereas guessing derived units isn't, as we see with angular velocity displayed in Hz or bending moments in Joule.

That's behavior isn't just maths doing something, but is concern about the the origins of the voltage laws, which, obviously, was mechanical (there are not multi meters at those times).

So, kg, m, s ... yes, that's natural that appear in mechanics, but electrons have their own mechanics too.

Working with units for those quantities is a big advantage for do the math in correct way.

Best regards.

Alvaro.