06-14-2016, 03:35 PM
Post: #297
 emece67 Senior Member Posts: 379 Joined: Feb 2015
(06-14-2016 02:16 PM)Claudio L. Wrote:  Interesting that they use this notation to omit actual physical units. 3k3 = 3.3_kΩ and 100p = 100_pF. But do they use this notation to actually perform calculations?
Let's say your result from a calculation is 3243.54534_Ω (or just the number, forget the unit). I don't see an easy way to display it, it would look like 3k24354534 ? or 3.24354534k?
The first one looks like an integer at first sight, as the letter gets lost in the numbers so while it might work for display of final numbers (like resistor values, all rounded and neat), it's not very good for general number display. The second form is doable (it's relatively simple to replace the ENG exponents for a single letter).
There's a lot of room for confusion, though, as 100k looks very similar to 100_K, same thing for 100m and 100_m. There's also the issue of which prefixes to use (all 20?). If I read 100a on the screen, I don't personally know what that means, unless I go to an SI reference table to see that a = atto = 10^-18.
There's also a prefix E = exa = 10^18, which looks like I forgot to print the exponent:
100E and 100E3 are quite similar.

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.

As a side note. The "complete" use of this notation (as I know it) is this: the dot/comma is always replaced by the prefix and the unit is appended at the end (eg. 3u3F is 3.3·10^-6 Farad). If the prefix is 1, then it is replaced by a letter identifying the magnitude (and using R instead of $$\Omega$$ for Ohms, thus 3R3 means 3.3 Ohm and 2H2 is 2.2 H).
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