Hi Jim,
What I am trying to achieve is to create a depth from a common plane / point which is the collar of a drill hole.
If ID=ID (from the same hole) and From = 0 then RL(value where From = 0) - RL .
I have update the file to better reflect the question, also i added a column Expected_outcome to show what i am trying to achieve.
ID is the drill hole name
From is the depth from the collar at surface
RL is the height of the point with respect to sea level.
Depth_From_0 would be the depth below the surface where From=0 and the corresponding RL