The AM Forum

Hmmm... are you sure it is 1.058201058201058 and not 1.058201058201059??

Jes' checkin'...

                      _-_-bear

Significant digits.

http://www.usca.edu/chemistry/genchem/sigfig.htm
http://www.usca.edu/chemistry/genchem/sigfig2.htm

In mechanics and physics a bunch of digits may be important.  We always viewed 5.938729 amps as the sign of a beginning EE student who has done too much Spice and not enough lab work. 

In electronics, most of the equations are approximations anyway due to real-world component and measurement tolerances.  For this reason specialized slide rules and nomographs worked pretty well for many things.

I always thought including way too many digits might mislead those less familiar with the art.

Chris

Then there is measurement uncertainty and error. I always wonder about claims of tenths of dB in measurements. They are pretty hard to make once, let alone repeat. Usually  they seem too good to be true. Of course this has nothing to do with toroidal transformers, which are a very good idea. If anyone cares to discuss the digits stuff further, let's start another thread. My apologies to the original poster for the hijack.

In the oil and natural gas reservoir business, had a professor that said that a 6 inch slide rule accurate to 5 percent would be sufficient given all the variables and quasi unknowns that occur downhole.  ;D

Quite PC given the hysterical standard of today, but he also said that every well was like a woman...   Each and Everyone different.

My brother loves to tell the story of how his professor illustrated the issue by reading the weight from a box of Keebler cookies: something like "12 ounces (340.194 grams)".

On the last day of class, the professor walked in to find a genuine Keebler Elf sitting in his chair. He didn't get it.

Bill, W1AC

I recall a lab class in engineering school (1967) that had us make measurements with 1000 ohm per volt meters and ammeters with one ohm and larger shunts. The idea was to learn the effect of the measuring instrument on the value being measured. And all calculations were to at most three digits on a sliderule, or by using a book with tables of logarithms in it. Out of a class of 100, there were seven Hams. It was a riot to watch the geniuses in the class go up to the stock room looking for a 3.789K resistor.

There was an old joke, about two university students, a math and an engineering major, they had an unfortunate event and found themselves in a hot place, in front of Ole Scratch himself.  They were both placed in a room with a single beautiful young woman standing at the opposite wall.  Ole scratch says to them, you can have the girl as soon as you cross the room, BUT you can only travel HALF the distance at a time.
The engineering student immediately runs half way across the room, the math student calls out to him, What are you doing? You'll never make it across traveling by halves. 

To which the engineer replies, true!  But in a minute I'll be Close Enough!!

Oh!

This was a reply post to another post where the first number I posted was an amount the OP put up... no idea how it ended up in its own thread?

But there it is.

                   _-_-bear

Maybe too many windows opened at the same time. Or, maybe it was just magic.

If the equations, and their applications are correct -- then wouldn't such calculated values yield a more accurate answer than measured values?

(Not that very many decimal places in the calculated value may be significant in the real world.)

RF

one would think so, but in reality, everything is just not accurate to so many decimal places.

take a 1k resistor for example,  mostly they come in some tolerance from 25-5% So you measure that, well how accurate is your digital (analog??) meter?  Calibrated it lately?  Fresh batteries?  Good leads?   

and for 99.9% of the folks in this world, 1K0 resistor that's really 850 - 1K2 or somewhere in between isn't that important. Folks who need that accuracy buy the 1% jobs and pay the premiums.

I can remember much younger students in a class I was in (I was the one with the white hair) amazed that I could finish the circuit labs so quickly.   They wanted to know how I could find those exact values specified in the problem (yea like the guy who wrote that text book ever even LOOKED at a standard resistor or cap value chart).  They were mortified when I said I just combined components on the fly to get 'close enough' values.  Pretty easy with caps and resistors in simple AC/DC circuits. My boards were a bit "ugly" but they worked.

Then they were like, yea but you got all the right answers...   and I really didn't know what to tell them (well it was an introductory course).   

Mathematicians generally worry about the 397th decimal place, Engineers are ok with PI being 3.1415-ish.