No, it’s not really like that. In metric, it’s not all that unusual to use 4-digit numbers. The elevation of Mt Everest is 8848 meters. AA rechargeable batteries are usually around 2000 mAh capacity. The Toyota Prius is 4540 mm long and weighs 1365 kg.
Although they really should stop at 4 digits - battery packs with 13000 mAh or even 26800 mAh are ridiculous.
I would think that it’s meant to address the situation of the OP, but in reverse. It’s for people who have mA-labelled devices they need to power, and don’t realize that 5A is sufficient for their 500mA load.
:eek:
Because the unit normally used is mA. If every item uses not just the same unit system but the same units, it’s a lot easier to compare, combine and in general use multiple items. It’s not just about labeling the specific item, but about making sure that it will get properly arranged between those which are 4800mA and 5250mA, rather than right beside the 5mA because “well, this one is 5 and this one is 5 so it’s the same, right?”
(Disclaimer: I once tried to teach 4th-grade arithmetic to people who couldn’t understand that 1/3 is smaller than 1/2. 3 is larger than 2, therefore one third is larger than one half, QED, and utter confusion when doing pie-slicing exercises. They could do the pie-slicing but they couldn’t relate it to the fractions.)
That’s because the arrow represents the holes moving not the electrons…
That’s not necessarily true either. E=IR is V=AΩ
(could have sworn I posted this earlier)
Sometimes (often?) Capacitors are rated at say 4700µF instead of the equivalent 4.7mF
Brian
As a rule of thumb, the preferred prefix is usually the largest prefix that can be used without incorporating a decimal for most common items in whatever set is being measured. Decimals are harder to read than digits for many people, especially in tiny print (or in an obscure color code). Since it’s not unusual to have power supplies rated at less than 1 amp, milliamps are the unit of choice.
Capacitors tend to get broken up into ranges–you will see some rated in nanoFarads and picoFarads, but otherwise µF is dominant. (I have seen special-application caps rated in Farads, though.) Inertia plays a part; once people are in the habit of using a particular prefix in rating a type of item, they tend to stick to it unless it becomes really annoying. Saying “Point zero-zero-zero-five microFarads” gets annoying very quickly, though.
OK, Balance, that makes some sense. The whole concept “avoid decimals if possible” is new to me. Being in the US, my most common use of the metric system is mostly around tools, where it is not at all uncommon to see a wrench/socket sized, for example, 7.5mm.
To be clear, it’s the decimal point which is hard to pick up when printed on the side of a tiny ceramic cap. But you need a chart, or a capacitance meter, or a ton of experience to read random capacitor ratings.
Well, manufacturers are probably more inclined to avoid decimals when the print is smaller than you typically see stamped on tools. I grabbed a random power supply from a drawer and a socket from the garage and measured the print, and the type on the socket was 3 times larger.
Disclosure, however: the power supply rating made a liar out of me–or at least highlighted that labeling is inconsistent–as it was rated as “0.5A”. It’s still not easy to see a decimal in a 3.5-point font, but the leading 0 made it obvious that it was there. My rule-of-thumb may be wishful thinking. 
Don’t forget the weirdos who measure capacitance in centimeters. :eek:
What? No more E for electromotive force, as in E=I x R, or P=I x E?