Hello,
I built the Roland SH-2 filter and it works well so far! However, I wonder if I did the “resistors” 2R2K and 5R6K correctly!
Are they resistances or inductions?
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I believe that the R is used in place of a decimal point. So 2.2k. This was a common convention from the early days of printing schematics as a decimal point could sometimes be obscured due to poor printing fidelity. Putting a R at the front is an early alternative to the ohm symbol so R22 denotes a 22 ohm resistor. This can cause confusion with a schematic numbering of resistors and became obsolete as printing improved.
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Ok, thank you for your feedback! Your explanation makes sense
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More commonly some people like to use 2k2 which makes me cranky. For no good reason, but I don’t need good reasons.
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There is worse. People actually pronouncing μF “you ef”. Effing terrible 
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Steady! I feel a long list coming on!
basically they are resisitors 2.2k and 5.6k not inductors at all
It is easy to miss the “.”, so writing 2K2 sort of eliminates one source of confucianism. I also write 2R2, instead of 2.2 Ohm.
But that’s me.
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I’ve also gotten into the habit of writing with 2K2 instead of 2.2K. On old circuit diagrams and then copying them poorly with a copier, it sometimes happens that a comma character disappears
Just make the dot big and dark enough.
2⬤2k. No problem.
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Or … Take a look at an E (exponent) series standard resistor table which is where I learned all I needed to label all my resistor drawers. It turns out manufacturers agreed to this logarithmic value scheme so manufacturers could make and service electronics reliably. Depending on how precise your application needs to be will affect how many distinct values you can have in a decade. The 1% 5% nonsense is just ass covering for manufacturing. I was told that there are reliable patterns of resistor ratios that occur in many common circuits but my brain can’t see it.
So, to loop back, if in doubt then giv’s a shout 
You can use a few 2R2k in an R2R, but you maybe shouldn’t.
It seems that Ω became R at some point, because of the inability (or inconvenience) to swap between scripts in typewriters. I guess R looks the closest to Ω in the latin alphabet? (Only that it doesn’t really, those who are older and academically inclined may have noticed that libraries stylized Ω as Ō in their catalogues).
At some point R became r, which is even more confusing, because r does not look anything like Ω. And the confusion is ongoing as confirmed by our forum! 
I don’t think that’s the reason. I’m pretty sure R is just used because it’s the first letter in the word “resistance”.
Indeed, that could well be the reason, but I am not sure. If it was, μF would have been given in latin script as “c” for capacitance, which is not the case. It is given as “u” because, ostensibly, u looks like μ.
But µ doesn’t mean “capacitance”, it means “micro”. And you couldn’t substitute m or M for µ because those already mean milli and mega respectively.
Part of what makes it confusing is the practice of omitting Ω when denoting resistances at least above 1 kΩ. Which also is probably related to the fact there’s no Ω key on a standard English keyboard (and it’s the only such common SI unit with a non Latin abbreviation). Instead you say 1 k, except it’s usually closed up to become 1k, and suddenly the SI prefix has become a suffix. Then if you write 2k2 it’s become an infix. Sometimes the F is likewise omitted from capacitances, but not as ubiquitously.
In formal scientific writing the space and unit are there: 2.2 kΩ, 4.9 µF, 100 mV. And yes, the k and m are lowercase (unless you mean megavolts) and the F and V are uppercase (even though the words farad and volt (and ohm) are lowercase (even though they derive from the names Faraday and Volta (and Ohm))).
Apples to oranges. μ is a prefix, the unit is F. There is no need to replace it with another letter because F is already a latin alphabet. The capacitance equivalent of 2R2 would be 2F2.
Edit. Oops @analogoutput was faster than me.
People probably decided to use R because it’s easier than typing kg⋅m2⋅s−3⋅A−2
Cheers
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Just incase anyone is interested…
The ASCII character for the ohm sign (Ω) is ALT+234 on a Windows computer.
On a Mac, you can type the ohm sign by pressing ⌥ Opt + Z.
Now, let’s all get back to making sounds and sharing understandable info. Yes this modern world has much change and many legacies that are confusing to the uninitiated, (some drive me a little nuts), but it’s more fun to explore and invent than it is to be hung up on the minutiae of proper form.
I’ll get my coat
And on Linux, there’s an English-Macintosh keyboard layout available, which can be used with any normal keyboard, and it took me years of struggling with special characters and diacritics before I found that out. µ is Alt-m, Ω is Alt-z.
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