Back in the old days, API-610 and CAESAR II used a right-handed coordinate system with the "Y axis" vertical.

Then, in the 8th Edition if I remember correctly, API-610 changed their coordinate system so that the "Z axis" is vertical. So we changed our API-610 module to perform this coordinate transformation when you click the [Get Loads from Output] button.

Then, in Version 4.30, we added the capability for users to define which axis (Y or Z) was vertical in piping jobs. As a result of this change, you will find the "Z axis vertical" checkbox in a number of places in CAESAR II.

So, for your API-610 analysis, if your piping was analyzed with "Y vertical" you don't check the "Z axis vertical" checkbox, and CAESAR II will perform the transformation. If your piping was analyzed with "Z vertical", you should check the "Z axis vertical" checkbox, and the loads should come straight across without any transformation.