deciphering meters

[mimicry]

any mathmaticians in the house. Can anyone explain where a decimal goes after you do the math? for example What is the focal lenght of an -9.00 D lens in cm? I get .11111111 now would it be 1.11 or 11? what determines the position of the decimal? as you can tell, I'm not familiar with the metric system. thanks in advance--ed

[Jeff Trail]

The formula for focal length is

D=1/over F D for the power in diopters and "f" is for focal length (1 f for meter)
(f 100 for cm) (f 1,000mm)

your example of -9 in cm

D (-9.00) 100cm/-9.00=11.11

or reversed 100/11.11= -9.00

Is this what you was looking for? sometimes it's hard to post formula's on the web since you can't write it in proper form

Jeff "math is my weak point" Trail

[shanbaum]

I think the answer to your question is in Jeff's post, but it seems to me that what you were really asking was, "how many centimeters are there in a meter?"

To which the answer is, 100.

The operative formula is F = 1/D; F is the focal length expressed in meters, D is the power expressed in diopters.

It may help to remember that "diopters" are frequently defined as "reciprocal meters".

[Dave Nelson]

1 meter=10 decameters. 1 decameter=10 centimeters. 1 centimeter =10 millimeters. Each decimal place is a ten value. thus, each time you convert from 1 to the other, you move the decimal place 1 over. 250 centimeters is 25 decameters, or 2.5 meters. 2.00D is a .5 meter focal length: 1 decimal place for decameters, 1 more for centimeters, and one more for millimeters. .5 meters=50 cm or 500 mm. Hope this helps. by the way, Canada has been metric for more than 20 years and I STILL dont know what the tempature is outside until I mentally convert celsius to farenheit.

[Blake]

Originally posted by Dave Nelson:
by the way, Canada has been metric for more than 20 years and I STILL dont know what the tempature is outside until I mentally convert celsius to farenheit.

That's exactly why the U.S. hasn't adopted the metric system yet. We're too used to buying a gallon of milk, or a pound of flour. Besides, can you imagine how much it would cost industries like the auto makers to convert their tools!
With that said, after 3+ years of learning more SI units (metric sys) than I ever dreamed of, I must say it's a better system than the British units. (I will admit I'm glad that "metric time" never caught on)
A lot of metric units are named for famous people (Newtons, Ohms, Hertz)... maybe we could start a drive to get Diopters renamed for a famous optician. Don't everyone jump to nominate Darris just yet, because the person has to be dead, and I don't think he's ready for that.

Blake

[Pete Hanlin]

<FONT COLOR=#FF0000>"Besides, can you imagine how much it would cost industries like the auto makers to convert their tools!"</FONT>

Actually, most US produced cars have a hodgepodge of metric and English gauged parts. Recently, I replaced the A/C unit in my truck. It amused (i.e., frustrated the heck outta) me to find that the nuts and fittings I took off required 3 different metric sizes (10mm, 15mm, and 7mm) and 4 different English sizes (1/2, 5/8, 9/16 & 5/4"). I guess it's like eyewire screws... why make one size work for many applications when you can make hundreds of sizes for one. Auggggh!

Pete

[Maria]

Don't worry - the european union is forcing us to go metric, and anyone selling goods in pounds and ounces gets threatened with legal action. Which means that english cooking, already famously bad, is now getting even worse, 'cos no-one can work out how much ingredients they have bought. I don't even know how much I weigh, as thats all in kilos now!

Maria (I don't care what Blair says, I'm not joining the Euro) Kelly

[mimicry]

thanks for the replies. I myself have a v.w. and along the way many u.s. made cars. I have both sets of standard and metric tools. Believe me, it's a hassle somtimes. I'm glad there's not a third system. Also, some cars do have both kinds of parts where you need 2 sets.---ed