Parcel area table rounding 'errors'

[Anonymous]

I'm  using parcels to delineate the drainage basins for my pre and post development maps. Both the pre & post sites have a total area of 86.85 Ac. When I place the parcel area tables containing the individual basins, the (3) pre-basins total 86.85 Ac, but the (54) post-basins total 86.88 Ac. I'm certain that this is an issue with converting SF to Ac and rounding, but I can't figure out how to get the tables to agree short of exploding them and 'tweaking' the individual basin/parcel areas.

Is there any reasonable straightforward way to achieve this without spending a lot of time chasing down the error?

Thanks,

~g

[troma]

How are you getting those totals? Adding up yourself on a calculator?

It only takes three out of your 54 parcels to measure just over the 0.005 mark to make them read 0.01. With 54 parcels you are more likely to see this than with three. It is not an error—it is C3D doing what you've told it to do.

Or is there more to it than that?

[Anonymous]

The pre site and the post site both indicate 86.85 Ac when right-clicking on the parcel tree in prospector and selecting properties. This is the size of the entire site(s).

The parcel area tables have a row for each sub-basin. There are 3 pre-development sub-basins that add up to 86.85 Ac and 54 post-development sub-basins that add up to 86.88 Ac. It's the discrepency between the site area of 86.85 and the cumulative parvel area of 86.88 Ac. that is the issue.

Thanks for the response,

~g

[BrianHailey]

"2+2=5 for very large values of 2."

This is the issue you are having. You can either live with the fact that Civil 3D rounds numbers or you can bump up the precision.

2.4+2.4=4.8 Round each to the nearest 1 and you get 2+2=5.

In the same line of reasoning, 2+2=3 for very small values of 2 (1.6+1.6=3.2).

I suppose if someone calls you on it you could always do something like this: