This is a weird one. I'm working on utility pipes, getting elevations and structure tops. I have found that when calculating geometry, or sometimes transferring numbers with the field calculator, the elevation number I expect is off by **exactly** -0.0000235 feet.

I'm using Virginia State Grid North for the XY coordinates, and NAVD_1988 for the z values. What I'm doing doesn't require a precision of more than 2 decimal places. But I still wonder why this comes up.

Is there some mathematical significance to this number? Have I found the question to life, the universe, and everything?

1. Coordinates never get stored in English units, only in meters, so conversions happen.

2. The Z resolution you have chosen allows this level of movement to be considered the same as an exact value.

3. Z Resolution establishes a Z grid and the Z extent sets an upper and lower bound of possible coordinates, and sometimes this makes it impossible to make whole number coordinates. Check and report these settings.

4. The projection chosen for Z may apply some adjustments when combined with the chosen XY projection (although that is a black box to me so I am not sure how they may interact).

5. Base 10 to base 2 conversions.

6. That distance is less than 1/10th the width of an average human hair and is such a small amount of measure variance from your reported benchmarks that it clearly falls within the tolerances of standard Survey procedures.