[time-nuts] Ultra low phase noise floor measurement system forRF devices.

Chuck Harris cfharris at erols.com
Sun Apr 1 14:35:59 UTC 2007


Didier Juges wrote:
> In France, and I suspect in the rest of the world, machinists talk in 
> 1/100th of a mm (centieme in French). The 'centieme' is a very good 
> fractional unit when dealing with hardware. It is not harder to talk in 
> 1/100th of a mm than in 1/1000th of an inch. 

Talking isn't the problem, actually machining to 1/100th of a mm is the problem.
Machinists, and the machines they use, run out of steam around a thousandth of
an inch.  1/100th of a mm is a practical impossibility for a lathe, or milling
machine to achieve.  But 1/10th of a mm is too course for operations involving
fit (bearings, press fits, ...).  So you end up counting in 4/100ths of a mm,
rather than 1/1000ths of an inch.

Cutting threads is a real nightmare with non CNC metric lathes, but super
easy with non CNC English lathes.

> 
> After 33 years in France, and 22 here in the US, I must say I have not 
> completely converted, by a long shot. The Imperial system is just too 
> ridiculous. It is an offense to common sense. BTU/hr? please spare me :-)

I'm puzzled about why that particular arbitrary constant bothers you.
A BTU is the amount of energy necessary to raise 1 cubic foot of water 1F in
temperature.  A BTU/hour takes one hour to raise the temperature of the water.

It is no more, or less, arbitrary than the calorie, but it is a whole lot less
wierd than a calorie/hour, or a kilometer/hour for that matter.

Life will always be a blended system, unless you decide you want a metric day,
metric week, metric year... I don't think that nature will accommodate you very
well.

-Chuck Harris




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