B: "Oh, come on -- it's just deciBels referenced to a milliWatt. +30 is one Watt, the power doubles for every 3dB increase, 10 x for every ten dB. Easy."

A: "I'll never remember that!"

B: "Okay, it's basic, just like in school, 10 log (P1/P2), right? And you know the reference is a milliWatt, so all you do is work it backwards, simple algebraic manipulation."

A: Deer-in-headlights look, "But I never

*took*algebra."

B: Slowly, "Divide the power in dBm by 10; raise ten to the result and divide the answer by a thousand, done."

A: Utter panic. "Can't you make us a chart?"

B: Defeatedly. "A chart. Sure. I'll do that."

C: (to A): "Or you could just use a smartphone ap. That's what I do."

A: "What if I don't have my phone?"

B: "What if you lose the chart?"

* * *

The chart is posted -- printed on a self-adhesive plastic label, stuck right above the offending "dBm" readout. Do you suppose they'll catch on that the the "Watts" digits repeat every ten dB with the decimal shifted?

...Yeah, me neither.

## 23 comments:

if (never took algebra == can't read)

taxes_on_who can++;

I confess when I joined a shop that used dBm it took me a few weeks to get used to it, but at least I knew how to do it and I knew I'd have to anyway so I sucked it up and did it.

What was almost comical was watching all the freshly degreed Computer Science grads the company had just hired trying to figure it out. The sad part was all the attenuators that died in the process:

"Why is my amplifier shutting down?"

"It says SWR warning. Do you have a load on it?"

"Yeah, a 30 dB attenuator and a dummy load." Points at a 5 watt coaxial attenuator and a 5 watt load.

"Um, you probably blew out the attenuator."

"Why? 30 dB down from 50 watts is 50 mW. Both the attenuator and the load should be able to handle that."

"So where's the other 49 plus watts going?"

"It's attenuated!"

That's why I was an 11Bravo10.

Mike

Loved it.

And for added giggles:

1) "Your cellphone just died and your mother has been hurt in a car accident in ___. Find ___ on a map, and drive there-no GPS."

2) During a power outage (no cash registers), take a $20 bill into a store, buy something worth 15.87 tax in, and see how the young counter person makes change. He has no electronic calculator today.

Do not register surprise when he hands you a $5.00 bill as change because he can't do it correctly and the fiver is "close enough". Store owner may not agree.

Re John,item 2)...We were on our way to the shop,and stopped at a fast food joint for coffee.Inside,the lights were off ,and the clerks were huddled talking to each other."Sorry,the power's off,we can't serve anything."But,we just want coffee.

But,the registers aren't working.One clerk(the oldest-I'm guessing a retiree working part time)took our order,wrote out a reciept longhand-showing the math-and counted out change.The kids were astonished.

That will be the end of civilization;OMG,I can't do math!!

"You're a better man than I am, Gunga Din."

"Never underestimate the power of Human Stupidity."

"You're a better man than I am, Gunga Din."

"Never underestimate the power of Human Stupidity."

"But math is hard!!!!"

This is why we can't have nice things.

I switched to LKFS.

Like "A" I'm still confused, do you have the chart and formulation in a simpler media? Like crayola??

My wife was teaching a basic bookkeeping class some years ago, and noticed one student just sat there doing nothing while the others were working a problem she had given them. The student wasn't able to do anything, she said, because she didn't have her calculator with her. When my wife handed her a pencil and said "Try using this one", the girl became confused and looked at her as if she was crazy.

These days, I'm shocked when someone actually counts back change the way nearly everyone was trained to do back in the old days when the register didn't do it for you. I actually learned to do that before I had even had my 1st retail job. I also sadly admit that I was better at doing fractional arithmetic in my head in 3rd grade than I am now.

One of my current peeves is the way "do the math" has crept into the language. I encounter this at work, where, if I point out an error in fitting 162 inches of cabinetry on a 145 inch wall, I get the response, "I did the math, and I don't understand this." I have as yet withstood the temptation to respond by asking why someone is using calculus to verify simple arithmetic. (Yes, I realize that 'math' is an indistinct term. The presumption of expertise is the annoyance.)

As long as I'm commenting, I suppose you're familiar with http://www.tubebooks.org/ -- but just in case, there it is.

Turk, me too, but not for Ku band RF!

While this sort of thing makes me weep for the future of our country, it makes me VERY confident in my own prospects for continued employment. Yes, I may be insubordinate, bad-tempered and generally hard to deal with, but I can read, write, AND do math without freaking out over it.

Dr. Jim, are you sure you;re not me? "insubordinate, bad-tempered and generally hard to deal with, but I can read, write, AND do math" hits pretty close to home -- though my arithmetic is so lousy I do freak out a little, double-checking that I haven't subtracted two from five and got seven.

TURK: In re LKFS, do you have the kewl "radar displays?"

I particularly enjoy handing the cashiers whatever pennies are needed to "make it even" just to see their brains explode, since they already entered the amount in their register. Two or three cents is enough to stop 'em in their tracks.

Would LOVE one of those "radar displays"!

Alas, they won't plunk for 'em. They make us calculate DialNorm with slide rules. Slide rules!

Re: Making change. Been there, seen that. If it hadn't been so horrifying, it would have been entertaining.

I, too, am shocked when someone actually counts back change like they're supposed to. I learned that in 3rd grade. We even had fake bills and plastic coins to practice with.

Hell, I think it freak 'em out when I give them 7.18 for a 6.68 sale. And the machine serves up the right amount of change FOR them. But who wants to carry all that loose change? Two quarters is bad enough.

To their credit, though, most of them never ask, "How did you figure that out?"

M

I ran into that when I worked at a big famous engineering company. The guy who wanted his jr. tech build a 10 Watt CCS RF amp using a single 955 could not wrap his mind around log scales. Or the fact that 10 watts out of a tube with 1 watt of plate dissipation is not good for tube life.

It was always fun watching the glass melt, though. But it was always my fault, so I moved on.

Stranger

The really sad thing is that it is not the kids' fault. They don't know that they are ignorant and under-educated.

It is really "our" fault. We allowed the new fads in education, so it is not really fair to sneer at the kids who can't do basic math, write a coherent sentence and make change.

We don't teach arithmetic and math is a reserved mystery.

The examples given are pure facepalm.

To this day I run into engineers that haven't a numeric clue. Ah well, maybe because I had to learn how to use a slide rule.

Eck!

jed said...

"These days, I'm shocked when someone actually counts back change the way nearly everyone was trained to do back in the old days when the register didn't do it for you. I actually learned to do that before I had even had my 1st retail job."

My first "retail job" started when I was 10 - selling the lunch tickets for my elementary school. I think I'd long since learned about counting out the change from observation, but this considerably improved my arithmetical speed and accuracy. (I was fantastic at math theory, but lousy at the details.) It also gave me a healthy respect for the book-keeping side of running a business; accounting is mathematically simple, but weeding out mistakes until the books balance is a bear. Apparently Blaise Pascal invented the first calculator in the 1600's when drafted into keeping the books for the family business, and I can certainly see why.

Calculators? This was 1963. They cost too much for ordinary people, and especially for schools, so you had to learn to use pencil and paper. Accountants typically used calculators that only added and subtracted by counting up and down on a row of number wheels, and learned tricks to multiply by repeated addition. Scientists and engineers with a need for more accuracy than a slipstick could buy (for about as much as a new car) a mechanical calculator from Frieden, that looked like Rube Goldberg had crossed an oversized calculator with a typewriter - except it was as sturdy as a tank. If you couldn't afford that and had to do a lot of multiplication or division at high accuracy, you'd buy a fat book of logarithms and multiply by adding the logs.

For a little more, you could get the Frieden model with extra cams and gears to extract square roots. (The algorithm looks sort of like long division.) For trig functions, logs, or navigation, you looked it up in a book of tables, and if you were into anything seriously mathematical you'd learn to gain one more digit of accuracy by interpolation in the tables.

Maybe they ought to teach the slide rule to everyone in the 8th grade. This requires estimating within about +/- 30% in your head (to place the decimal point). It teaches you that exact numbers are usually unnecessary (and there is no such thing when you start with measurements), and gives you experience in estimating how much precision is really called for. And you stare at a physical representation of logarithms all day. But for that to work, we'd need better math teachers from the first grade on.

But the biggest problem with math in school systems is that there are a fair number of kids that are never going to get it. It holds back the kids that did get it. And then many of the ones that didn't get it become teachers, while the mathematically adept can get "real jobs".

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