[sdiy] Wavetable info

[Magnus Danielson]

From: "Oakley Sound" <oakley at techrepairs.freeserve.co.uk>
Subject: Re: [sdiy] Wavetable info
Date: Fri, 2 Jan 2004 09:33:54 -0000
Message-ID: <01c501c3d113$9ace48e0$6570fea9 at oemcomputer>

> > You cant choose between capital and normal letters as you feel like,
> > they have different meenings. This is important for both the units
> > themselfs as well as the prefixes.
> 
> This is true... but there is T, T and T. Tesla (unit), Temperature
> (fomulae) and Tera (multiplier).

Those is distinct by thier scope. It is interesting enougth not a big chance
of us seing measures like 1,2 TT (TeraTesla) since 1 Tesla is LARGE as it is.
T in a formula is to be used only for absolute temperature, that is Kelvin
degrees.

> I think the usage is the dominating discrimanator here, especially amongst
> friends. :-)

Well, it was like a friendly side-comment that I wanted to point this out,
since now somebody copied the misstake of another person, not leading to a
very usefull habit. It's not hard to use those few darn units we use properly,
so let's do that.

> > For instance, a k means the kilo prefix, where as K means Kelvin.
> 
> Whilst true I have always thought that this does make for some
> confusion. I think K is the only multiplier over 1 that exists in the
> lower case. G, M and T being the most common others. Also annoying for
> the unwary, the kg is a base unit and not the gramme.

Yes, this IS an annoying detail and inconsistency. By the time that things
where put into a even more structured order a few things where to late to fix.
However, this inconsistency is well documented and the appropriate format is
international standard.

> In primary school I learnt with the CGS system (actually c.g.s. standing
> for centimetre, grams (sic) and second where these were the base units)
> but the UK educational system moved over to the SI in the 1970s.

We got to learn the SI system in school, essentially in full compliance with
ISO 31.

While BIPM holds the official SI system document (which has one official part
in French and an official translation into English) it is ISO who has the
international standard to be used in practical engineering. This is the ISO 31
suite of standards. In the ISO 31 suite there is several standards, detailing
terms, units etc. for a number of different engineering fields and being an
expansion of the BIPM SI document. The BIPM SI document is more interesting in
a meterology sense (meterology is the science of weigths and measures such as
the meter ;). Unfortunatly the ISO 31 suite is not available for free and
buying the real standards cost more than what a normal private person is likely
to spend, but there is a book from ISO containing them all, which is quite
decent in price, so there might be something of an interest. Darn! I forgot to
ask Santa for one this year too... :P

> For more information:
> 
> http://physics.nist.gov/cuu/Units/checklist.html

You can get the hard facts of the SI system by downloading the "SI brocheur"
from BIPM (http://www.bipm.org) in PDF-form.

There is a US-version from NIST known as Special Publication 330. This SP330 is
however an edited version in which various editing details has been changed in
order to be compliant with the US writing of numbers and spelling of certain
words (i.e. metre vs. meter). I do not recommend reading of SP330 now that
BIPM put their official SI publication online.

Now, for a little meterology challenge:

a) How does it come that the inch became defined to 25,4 mm?
b) How does this deviate from what was thought as the previous inch definition
   at the time?

Cheers,
Magnus