HP35s any good for EE?

[emece67]

(04-17-2015 09:09 AM)walter b Wrote:  

(04-17-2015 12:33 AM)emece67 Wrote:  ... it also works with units, a capability I really miss in RPN calculators.

Please, would you mind enlightening me why you need that?? TIA.

Background: On our side of the Atlantic Ocean, people use SI units. Doing so, you can throw in any such units (V, A, Ω, F, T, Cb, ...) in an equation and the result will be returned in the corresponding correct unit - as long as the equation is correct, of course.

d:-?

Cause I work, many times, with old documents that use non-consistent unit systems.

Also, because I rely on unit consistency to check the validity of some calculations. e.g. Working with electro-mechano-acoustical systems, you have 3 kinds of Ohms ("classical" ohms, mechanical ones and acoustic ones), and 3 kinds of "currents" and 3 kinds of "voltages"; working with a big number of different magnitudes is easy to forget that you need to multiply/divide by some other magnitude to get the result you want (specifically, when you cross some "boundary" between the 3 domains: electrical-mechanical-acoustic). With an unit-aware calculator, if, after a long calculation with many different magnitudes, I get a force in N/m2, I instantly see that I've forgot to multiply by a surface, so I re-check my calculations. Note that this is a problem even if you are using the SI (as the SI does not make you error-free).

Also 2: because many modern (and old) documents do not clearly state the magnitudes they are measuring. E.g. some authors state the power loss in a magnetic core in W, but others in W/m3 and still others in W/m2, and the remaining ones in W/kg and, even more, some use J instead of W. But they do not clearly say what definition of "magnetic loss" they are using. Blindly using their equations without checking the units is a safe recipe to non working systems. As above, if you get the current across a coil in, say, A/sqrt(s·Kg), you know you have an error, somewhere, involving a mass and a time; perhaps you and the author you are consulting use different definitions for some magnitude involving a mass and a time. This is a problem even if you adhere to the SI (as the SI does not state what is the definition of magnetic loss in a core).

Also 3: because sometimes you are not calculating an equation you see in a book or paper, but you are creating such an equation and, of course, you cannot be absolutely sure that you have not committed an error. Checking unit consistency in such equation is a good method to be on the safe side. You can do the check manually but, well, I have a little machine that can do it for me!

Also 4: because in the previous cases (perhaps with the exception of Also 3), the approach of checking all unit previous to the calculations and, if any problem is detected, converting all magnitudes to the SI is, IMHO, not very practical.

Regards.

p.s. I think I'm at the very same side of the ocean that you are.

p.s.2. I also miss this unit-aware behaviour in other tools, such as Matlab. The Mars Climate Orbiter wouldn't have crashed using such tools (although the real problem here was some people did not adhere to the SI).