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Reviewer Does Not Understand Rounding  

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Posts: 709
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Years ago a wise Engineer I worked under went on a pilgramage preaching Significant figures. How I wish I still had a copy of his presentation. It was on the eve of laser distance meters. Some of us were actually reporting distances out to three decimal places because that's what they read out to.. I'm constantly educating Flood Plain Coordinators if the Base Flood Elevation was contrived using a forty foot contour map with a planimetered drainage area and a statistical rainfall figure. How can they be interpolating the elevation down to a hundredth or even a tenth of a foot.

The best RTK GPS system on the market today claims 1 centimeter accuracy. It's pretty tough to set a pin within three hundredths  of a foot and then we record our distances to a hundredth and our angles to a second when the equipment you're using isn't capable of measuring that precisely.

Reminds me of the days we would tap the rebar over a hundreth to set it exactly on the point we had chained to. Acreage is even less precise. But our CAD programs will spit it out to three or more decimal places so that's what we record on our Plats. 

I realize your boundary won't close flat, but you didn't survey it accurately so that it would. Unamused  

Posts: 5610
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Rounding the final answer to reflect likely accuracy is a good practice. But carrying every digit available while working up that answer is also good. 

I once watched a surveyor using EDM that read out to 0.005 ft precision (before everybody had a data collector) record those readings in his field book rounded to 0.02 because that was the required precision on the final plat. Angles similarly.

That gave him a lot more error to deal with in calculating closure, etc. Every rounding adds error, which may or may not be significant in a given situation.

Norman Oklahoma
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Posted by: @armichael

my boss says to just go with it, but is this ridiculous?

It is ridiculous. But your boss is right. We must choose our battles. 

Posts: 1259
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Had the exact same thing today. Reviewer asked why 100 and 100 added up to 201. I answered, "rounding". Got a blank look. Latest email said to fix the problem. I will round each parcel, then add them to get the total.

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chris mills
Joined: 8 years ago

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I'm not sure how you have to present your figures on that side of the pond, but I've had similar situations over here, where an area has been split up but each plot has to have a minimum specified area (say 4 plots of 1 acre out of a 4.1 acre plot - less the access roads).

I list the plots in a table, one column with decimals and one column with its rounded value (using headers "Exact" and "Rounded").

Only the decimal column gets totalled, to show the whole area - the rounded values are not totalled. I've had comments passed, but nobody has ever come back to dispute the overall area. Perhaps even the thickest understand it, laid out like that.


holy cow
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Encouraging professionals to lie.  What a great idea!

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