Atharv Joshi
Forum Moderator

Hi Alex, 

You can use "Retain Sketch" feature so that the Sketching Plane and dimesnions doesn't go away when you toggle to 3D Mode. 

Please check out the below video tutorial on annoation plane which can be helpful to define the dimensions. 

Annotation dimensions in SpaceClaim - Ansys Knowledge

Discovery SpaceClaim: Getting Started Tutorials - Ansys Knowledge

Thanks and Regards
Atharv