# One decimal off

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Hello:

I was working on tracking down benchmark EZ0638 which is listed with the following coordinates:

N 35 52.083 W 78 51.05 How do I determine the last decimal point on the west coordinate? do I just put it in my Etrex Legend as W 078 51.05 or is it .005? I went to the jeep.com converstion table http://jeeep.com/details/coord/ and put in the coordinates and I think I used the correct output, but I am not realy sure which is the correct one. what is the correct procedure for determining the three decimal point coordinates that my GPSr wants?

If it was me, I would say it was 51.050. It's not 51.005.

Good luck

Nil Satis Nisi Optimum

quote:
Originally posted by Jabba:

Hello:

I was working on tracking down benchmark EZ0638 which is listed with the following coordinates:

N 35 52.083 W 78 51.05 How do I determine the last decimal point on the west coordinate?

I'm surprised the latitude had three decimal places. W 78 51.050 is how you should enter the longitude. Incidentally, airports and aids to navigation are all still referenced by only two decimal places ... the third decimal place only amounts to a range of approximately 50 feet.

Note that benchmarks might be listed using a different (older)datum, and the coordinates might be only approximate.

quote:
Originally posted by BassoonPilot:

the third decimal place only amounts to a range of approximately 50 feet.

Are you sure????

I think it's time you read Markwell's FAQs!

Actually, I think it's the way you're wording it. I know better, but it sounds like you're trying to say the third decimal place makes 50 feet difference. It's probably just the way you people talk down south...

And yes, it is 51.050

Always proof-read carefully to see if you any words out.

What he's saying is: assuming the 51.05 minutes had been rounded off to the nearest 0.01 minute, it might actually have had a value as low as 51.045 or as high as 51.055. That's plus or minus 0.005 minute.

A mili-minute of latitude is everywhere 6.07 feet. So, +/- 5 mili-minutes of latitude would be a +/- 30.35 foot range of uncertainty.

A mili-minute of longitude is smaller than that of latitude by a factor of the cosine of the latitude. At 42 deg latitude, for instance, the cosine of 42 being 0.743, makes a mili-minute of longitude there be 4.51 feet. So, a 5 mili-minute range of uncertainty of longitude would be +/- 22.55 feet.

Using 2 decimals instead of three introduces a total search space of uncertainity which is 45 feet wide (E-W) by 61 feet high (N-S).

We ought to be able to find a cache in such an area. Of course there are other significant errors as well that are added to it.

[This message was edited by Don&Betty on October 05, 2002 at 04:22 PM.]

quote:

Are you sure????

I think it's time you read Markwell's FAQs

Markwell's FAQ contains excellent information, but much of it is of greater theoretical than practical value.

You may have noticed I used the word "approximately." Considering the several factors that affect the accuracy of gpsrs both at the time a cache was placed and our attempt to find it, I think "5 feet per (third decimal place) tick" is a close enough approximation for "field use" while geocaching.

I promise that the very first time I see my gpsr agree precisely with the posted coordinates of a cache, I'll reconsider ...

[This message was edited by BassoonPilot on October 06, 2002 at 08:20 AM.]

quote:
Originally posted by BassoonPilot:

... You may have noticed I used the word "approximately." Considering the several factors that affect the accuracy of gpsrs both at the time a cache was placed and our attempt to find it, I think "5 feet per (third decimal place) tick" is a close enough _approximation_ for "field use" while geocaching.

now being "approximate" would that be 5 feet per third decimal place in total or 5 feet per third decimal place both ways

Cheers, Kerry.

I never get lost everybody keeps telling me where to go

quote:
Originally posted by Kerry:

now being "approximate" would that be 5 feet per third decimal place in total or 5 feet per third decimal place both ways

"Yes"

(The latter; each way.)

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