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0 pointsTloewald11y ago0 comments

SI units don't include millinewtons, so the problem wouldn't arise. That's part of the point.

You measure mass in kg, not g, not tonnes.

You measure distance in metres. Not kilometers. Not nautical miles.

You measure time in seconds.

A Newton is a derived SI unit — 1 kg m / s^2

Incidentally, this is why engineering notation works the way it does. You pick your units and you get the significant figures from the mantissa and the descriptive prefix (giga, nano, micro, kilo, etc.) from the exponent.

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Ankaios11y ago

The SI units absolutely include newtons and millinewtons. The derived units (http://physics.nist.gov/cuu/Units/units.html) and prefixes (http://physics.nist.gov/cuu/Units/prefixes.html) are both part of the SI.

Also, remember, people are representing these numbers on computers. Derived units are very useful—in fact they are often critical to achieving necessary accuracies using compact representations. Further, representing quantities in terms of other unique, problem-specific units is often extremely helpful for ensuring good numerical behavior.

pimlottc11y ago

His point (I believe) is you always need to label units regardless of system. You could have the same problems with microseconds vs nanoseconds.

jjoonathan11y ago

Tloewald's point was that microseconds and nanoseconds are not SI base units, so standardizing on base units eliminates the ambiguity (the second alone is the SI base unit of time). Of course additional mechanisms of double and triple checking are probably still warranted to account for human fallibility.

jessaustin11y ago

That's fine until you start using floating point values in order to satisfy this SI fetish. (I guess you like farads and henries too.) It's much better to use fixed point and keep track of your multiplier. A sufficiently advanced type system could do this, but at some point it will require careful thinking about precision.

TloewaldOP11y ago

Using fixed point and tracking your multiplier is exactly like using floating point.

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pimlottc11y ago

Regardless of what you standardize, you still need to include the unit for any figure.

TloewaldOP11y ago

Yes but you eliminate errors when working within a type of unit. NASA's problem came from converting one kind of length to another. You are clutching at straws here.

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Ankaios11y ago

pimlottc11y ago

His point (I believe) is you always need to label units regardless of system. You could have the same problems with microseconds vs nanoseconds.

jjoonathan11y ago

jessaustin11y ago

TloewaldOP11y ago

Using fixed point and tracking your multiplier is exactly like using floating point.

1 more reply

pimlottc11y ago

Regardless of what you standardize, you still need to include the unit for any figure.

TloewaldOP11y ago

Yes but you eliminate errors when working within a type of unit. NASA's problem came from converting one kind of length to another. You are clutching at straws here.

j / k navigate · click thread line to collapse