06-16-2016, 12:32 PM
Post: #298
 Claudio L. Senior Member Posts: 1,885 Joined: Dec 2013
(06-14-2016 03:35 PM)emece67 Wrote:  Keep in mind that this is an (ab)use of notation by engineers. I fact no EE (well, most of then) cares much about numbers such as 3k24354534, they only want to know about 3k2, so the k is not missed. (You know, for EE people the volume of a cow, or any other animal in fact, is half the cube of the distance from horns to tail ;-)

I understand that many people will need to read the table to know that 2 aA is 2·10^-18 amperes, but my personal case is just the other, The machine gives 2·10^-18 A, then I convert it to 2 aA and this is "the value" of the current. I find many students lost when dealing with powers of ten until they start to think with the prefixes.

In any case, I asked for this notation (or the simpler one 2.34 k, or 2.34_k or whatever you think enough clear and easy to implement) as a display only capability accessed thru a combination of keys similar to that Vtile proposed to circle between different powers of ten in ENG mode (here circling between different prefixes). Forcing the machine to parse expressions like "0u1 ENTER 10000p +" in order to return 110n0 seems overkill to me. Perhaps for "heavier" use the unit approach "2.3_u ENTER 100_p +" can be better, provided the UNIT system can cope with non-dimensional quantities with prefixes but w¡thout units.

I think some clarity starts to emerge here. The unit system already supports prefixes (not without units though), however, it won't automatically convert to your preferred prefix.
I think the best compromise without breaking the rules of the SI system is to enforce the use of units but auto-convert to a desired prefix. If you are willing to type 2.34_k then 2.34_kF or 2.34_kA is not going to give you carpal tunnel syndrome.
When in ENG mode, I can try to display units using a prefixed unit instead of showing an exponent, so if your number is 3300_Ω, in ENG mode it will show 3.3_kΩ instead of 3.3E3_Ω (display only, the actual object on the stack remains 3300_Ω).
It's not exactly what you asked for, but this way it will work for all units, so other disciplines can also use this feature (nothing against EE :-).
If/when I implement the changing ENG exponent (I'm still not clear on how to implement it), it shouldn't be too difficult to implement this on units too.
I think it should be a "preferred exponent" that you can change at will (perhaps it has to be a separate mode, as ENG chooses the best exponent for you). For example, if your preferred exponent is set to 3, all number displays will be forced to display as NNNE3, and all units would be forced to have the k prefix.
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