netcurmudgeon (netcurmudgeon) wrote,

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Units of confusion

When I was in high school my chemistry and physics teachers used to hammer us about making sure we had our units right. If we were figuring DC electrical power and were multiplying Volts by Amps to get Watts, they wanted to see 6V x 3.7A = 22.2W. ...Particularly in physics when doing the math for kinematics. There's a world of difference between m/s and m/s2. One's an expression of velocity and the other is an expression of acceleration.

With this framework of particularity beaten into my brain, I have always been careful about units. And, it has always set my teeth on edge to see someone else bungle them. The most common slipup in IT is bits vs. Bytes. 100Bps (Bytes-per-second) is eight times greater than 100bps (bits-per-second). Someone telling me about their "hundred gigabit drive" is saying that they have a 12.5GB disk. Not what they mean, but that's what they're saying.

So, I got a good chuckle on Monday when an email crossed my path from someone out in the schools who was trying to tell one of my coworkers about a video conferencing system they want to put in. In one of her bulleted items she said:

• The video conferencing uses only 190-380 Kw/sec (which is also a good thing)

I know that she meant Kb/sec, because that's how we talk about bandwidth, and video rigs usually run in the 128Kbps to 384Kbps range. But think, for a moment, about what she said. 190-380 kilo-Watts per second. Watts are a power-per-second unit anyway, so the seconds can be discarded. That leaves us with — taking the high end — a video conferencing system that draws 380,000 Watts. A modern household electrical service supplies ~15,000 W. That video conferencing unit would be drawing almost twenty five times that amount of power...

The moral of the story is, my teachers were right: always pay attention to your units. Otherwise people like me will make fun of you. Or, worse, you might crash a space probe into Mars 'cause you mixed feet and meters in a careless communication.

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