Letter to Prospect Magazine

[fanf]

Pedantry about basic units... (I hope these URLs work.)

http://www.prospect-magazine.co.uk/article_details.php?id=6820&AuthKey=ffd48ae887d8c740d86a0d7354814dbc&issue=503

http://www.prospect-magazine.co.uk/article_details.php?id=6746&AuthKey=ffd48ae887d8c740d86a0d7354814dbc&issue=501

Comments

[ronebofh.livejournal.com]

I thought the gram was defined as a cubic centimeter of water at sea level at 4°C. What's this shrinking kilo nonsense?

[fanf]

It was originally, but that definition doesn't provide a sufficiently accurate repeatable experiment.

Metrology

[(Anonymous)]

If you define the kilo in terms of counting actual atoms as they whoosh past, you simultaneously define Avogadro's number.

Question: do you count radians as units? Think carefully.

CRB

Re: Metrology

[fanf]

The problem with that definition is that it isn't currently practical, i.e. you can't use it to calibrate machinery.

You can treat radians as a unit or as a ratio, depending on what's convenient. However a significant difference between radians and physical units is that they are defined mathematically rather than based on some experiment.