Field Calculator Conditional Script

Discussion created by gjohnson_btv on Jan 6, 2014
Latest reply on Jan 6, 2014 by gjohnson_btv

So I have a sewer Manhole attribute table with an "INVERT" field (measurement to the lowest pipe in manhole) fully populated with tappe down measurements. The next field over is "Invert Elevation" which has a few hundred values that have been manually calculated and entered by a contracted engineering firm from a previous watershed project (high accuracy data). Lastly, I have a DEM_ELEVATION field that has been derived from LiDAR for our city to give us elevations of manhole rims.

Now, my question is, can someone help me with the correct conditional statement to make sure I don't overwrite the values for "Invert Elevation" that are already calculated? For example

If the "INVERT" field contains a value that is not <Null>, then calculate (DEM_ELEVATION)-(INVERT)=(INVERT_ELEVATION)

Any help would be appreciated!