>> Frankly, if you're measuring something that's 10 meters across, do you
>> even *care* about the last 5mm? Probably not.

Depending on what it is, it's also probably going to change length with 
temperature. For example a 10 metre bit of steel could easily be 5mm 
longer in summer than in winter. Those 237 metre long trusses in the 
other link could be 10cm longer. The system will be designed to cope 
somehow with those changes in length, so the tolerances on those type of 
parts is not that critical.

> Not if you are measuring it in cubits Otherwise that is a terrible
> tolerance. For instance the first breakthrough from the English to
> French side of the Channel Tunnel was 358 mm out over 22 Km.

That's cheating though, that's like making your 10 metre bit of steel to 
a +/- 5mm tolerance, then filing it down to fit :-)

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