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# A rant on the usage of mW, nm and units in general

#### Bluefan

##### New member
I see this a lot when people post for the first time: "how many MW does my laser have?" A laser doesn't have MW's or nm's, it has an output power and a wavelength. So if you're wondering what power you laser is, ask this:
What is the output power of <some laser>
How many MW does <some laser> have?
And you will get a reply saying it's something like 100mW for example.

The same goes for the wavelength, ask this:
What is the wavelength of <some laser>
How many nm's does <some laser> have?
In case if most green pointers the wavelength will be 532nm. Current in ampere (A) or amp for short and voltage in volt (V) goes the same.

Also note the difference between 1mW (one milliwatt) and 1MW (one megawatt). It's the difference between 0.001W and 1,000,000W. Unless you run a huge goverment project, you laser will have an output power in the milliwatt range instead of the megawatt range.

So please, refer to quantities by their name, and use the appropriate unit in combination with a numerical value or something like that, but please don't use units like they are quantities.

The background info:
Physical quantity - Wikipedia, the free encyclopedia
Units of measurement - Wikipedia, the free encyclopedia
International System of Units - Wikipedia, the free encyclopedia
SI prefix - Wikipedia, the free encyclopedia

#### Ibuprofen200mg

##### New member
:crackup:, yep for those of us in the sciences stuff like that is borderline profanity...

#### daguin

##### New member
Now you know how the professors in your first couple of years of university feel :crackup:

Peace,
dave

#### Cyparagon

##### Well-known member

A for amperes (amps) W for watts, and m for meters. (note the case)
"Milliwatts" is abbreviated mW, not mW's. You don't see people abbreviating pounds as lb's or millimeters as mm's. Apostrophes do NOT mean "look out, here comes an S!"

Also, you ask for the current. You don't ask "how many ma?"
Similarly, you don't ask someone "how much feet are you?" - you ask "how tall are you?"

##### New member
Similarly, you don't ask someone "how much feet are you?"
I was asked that by a little kid just recently !
Then he had me lie down while he measured how many of his "feet" tall I was. (just over 35 of his "feet".)
It was educational and kind of funny at the same time.

#### hakzaw1

##### Well-known member
35?? really?
if his tiny feet were just 6" long that would make you 17'-6" either he was a tiny toddler or you are many many feets tall. lol

I guess thay call you 'Shorty' cause you are not!

hak

#### Fiddy

##### New member
Good idea, i hate it when people act like they know what they are talking about then get the units mixed up....something worth ranting over definitely.
the most common one i come across is people quoting power figures in mA or vice versa.

Also, in my learning curve i found it weird to getting used to the nm (nano meter) being the wavelength value as i have been working with engines and electric motors which use Nm (newton meters) which is the value for torque, so i found myself saying "this laser has a wavelength of 660 newton meters":twak:

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##### Member
@ Fiddy- Thankyou for teaching me about torque, newton meters, this is new to me.

#### Fiddy

##### New member
no worries mate :beer:

##### New member
I wouldn't normally be 35 of the little guy's feet tall but he wasn't walking a straight line and there was some tickling involved...

#### AJ Pierson

##### New member
this bugs the crap outa me too.

i used to work at circuit city and you wouldnt beleive how many people would ask "how many Mhz does this computer have?" or "well which one has more Mhz?" or "how much would it cost to get more Mhz for it after i buy it?":crackup:

obviously they had no idea what Mhz means, only that "more is better".