Mxsmanic wrote:
BT writes:

why does it need to be rigid?

It doesn't have to be, but in information theory, the more rigid the
encoding, the greater than transfer of information. That's why the
phrasing of ATC communications is so highly conventionalized. That's
why METARs and TAFs have a highly specialized format.

I believe the transmission of weather information by use of abbreviated
METAR codes originated in the days of 10 character-per-second Teletypes (or
possibly even earlier). The ASR 33 Teletype (the model I'm personally
familiar with) could only print uppercase characters. At that slow rate of
printing and usingg such a limited character set, brevity was an asset.

I first learned to program in 1973 using Teletypes as input and output
device. A nice picture of an ASR 33 teletype is he

http://www.catb.org/~esr/writings/ta...l/ch02s02.html