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Rounding....what say you?

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squirl
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Years ago, I heard some "surveyor logic" when it comes to rounding numbers. Is anyone here familiar with this logic or what I'm referring to? 

I remember it being somehow different than the typical rounding logic of 5 or greater round up, 4 or less round down.

Who knows, I could be losing my mind. It wouldn't surprise me.

T. Nelson - SAM

 
Posted : March 13, 2025 8:07 am
john-putnam
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For the purpose of design mapping, I like to round to the most conservative number.  For example, because flatter pipe slopes are more worrisome, invert elevations get rounded up to show a worst-case scenario.  Similarly, wire heights get rounded down because clearance is the typical issue.

 
Posted : March 13, 2025 8:19 am
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peter-lothian
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I think I heard something along the lines of "When rounding a 5: If the next leading digit is even, round up. If the next leading digit is odd, round down." I think it's intended to equalize the effect of rounding the 5 digit because it falls exactly halfway between 0 and the next "higher" 0. Always rounding up skews the resulting calculation, supposedly.

 
Posted : March 13, 2025 8:24 am
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BStrand
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@john-putnam Yep.  When I list an acreage just about anywhere I round down so worst case scenario the owner discovers they have more land than they thought they did.

 
Posted : March 13, 2025 8:48 am
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sergeant-schultz
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I round to the even number; 24.5 to 24, 23.5 to 24

 
Posted : March 13, 2025 10:45 am
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surv8r
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Several years ago, I had a reviewer reject a plat submittal because one of my lot acreages “was wrong”. The minimum lot size was “1.50 acres”. One of the lots calc’ed at 1.4995, so I rounded up to 1.50 acres.

The reviewer informed me that while numbers can be rounded down, they cannot be rounded up because “you’re adding something to the number that doesn’t exist”. (The reviewer had a handy-dandy cogo program and would run each lot).

Luckily, this lot adjoined a 4+ acre lot, so I “moved” the common lot line 0.01’ to make the acreage work… 😐

I can explain it to you, but I can't understand it for you...

 
Posted : March 13, 2025 11:45 am
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BStrand
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Posted by: @surv8r

The reviewer informed me that while numbers can be rounded down, they cannot be rounded up because “you’re adding something to the number that doesn’t exist”

But you can delete land that actually exists?  What a nonsense argument.  😆 

 
Posted : March 13, 2025 12:15 pm
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dave-lindell
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I learned to round to the even number so there will be no prime numbers to deal with.

 
Posted : March 13, 2025 1:05 pm
land_odse
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In geodesy, Gaussian rounding is often used
 
When dealing with numbers that have 3 decimal places, it works like this:
1) If the third decimal is less than 5, leave the second decimal unchanged.
2) If the third decimal is greater than 5, bump the second decimal up by 1.
3) If the third decimal is exactly 5, check if the second decimal is even or odd:
– If the second digit is even, leave it as-is.
– If the second digit is odd, round it up by 1.
The key difference from standard math rounding is in rule № 3.
 
Examples:
3.141 → 3.14 (1 < 5, just drop it).
2.715 → 2.72 (5 after odd 1 → round up to even).
1.235 → 1.24 (5 after odd 3 → round to even 4).
4.725 → 4.72 (5 after even 2 → keep 2).
0.685 → 0.68 (5 after even 8 → leave 8).
 
Gaussian rounding is used in surveying to minimize systematic error buildup during numerous computations. In my experience, I’ve run into software where rounding methods were configurable in the settings. Colleagues who slept on this had to redo their work multiple times
 
Posted : March 13, 2025 1:33 pm
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squirl
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Posted by: @peter-lothian

I think I heard something along the lines of "When rounding a 5: If the next leading digit is even, round up. If the next leading digit is odd, round down." I think it's intended to equalize the effect of rounding the 5 digit because it falls exactly halfway between 0 and the next "higher" 0. Always rounding up skews the resulting calculation, supposedly.

This sounds very familiar. I think you hit the nail on the head.

 

T. Nelson - SAM

 
Posted : March 14, 2025 6:13 am

squirl
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Good to know I'm not losing my mind...not yet anyway.

T. Nelson - SAM

 
Posted : March 14, 2025 6:15 am
james-fleming
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Posted by: @peter-lothian

"When rounding a 5: If the next leading digit is even, round up. If the next leading digit is odd, round down."

 

The abbreviated version that I learned years ago of this method was "Even-Up"

 
Posted : March 14, 2025 6:53 am
murphy
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Another name for Gaussian rounding is Banker's rounding.  There's a setting for it in Autodesk but I never found one for Carlson.  You'd think it would be mandatory learning in college but I only found out about it here.

 
Posted : March 14, 2025 8:44 am
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Norman_Oklahoma
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Posted by: @surv8r

Luckily, this lot adjoined a 4+ acre lot, so I “moved” the common lot line 0.01’ to make the acreage work… 😐

You could have moved the boundary 0.004' and probably achieved the same thing. The dimension label to the hundreth of a foot would not change but the area would. But battles of wits with the unarmed are rarely fruitful.   

 
Posted : March 14, 2025 11:05 am
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OleManRiver
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@peter-lothian We call that military rounding.

 
Posted : March 14, 2025 5:08 pm
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CV-Nevada
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@squirl 

That is how I was trained as an 82C. We called it "Artillery round-off". 

 
Posted : March 15, 2025 8:30 am
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thebionicman
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@cv In the mortar section we round both ways and send an HEQ to each..lol

 
Posted : March 16, 2025 7:15 pm
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GaryG
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what does the Q stand for ? 

HEQ ?  High Explosive ?

 
Posted : March 17, 2025 5:10 am
squirl
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High EQplosive perhaps? 😉 

T. Nelson - SAM

 
Posted : March 17, 2025 6:39 am
thebionicman
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High explosive, quick fuse setting..

 
Posted : March 17, 2025 6:54 am
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