Converting orthometric heights into ellipsoidal heights

Discussion created by njblokland on Feb 27, 2013
Does anybody know how I can add a field to the TOC with ellipsoidal heights. I have a table with coordinates in a projection and heights relative to MSL. Geografical coordinates can be added to the TOC by changing the coordinate system in the Data Frame Properties and then select Calculate Geometry after adding a new field. However, I don't know how to get a new field with ellipsoidal heights.