Technical How do you measure a spindle length?

That may be a noob question but I need to know how to make the difference between a '35 and a '36 Ford spindle, I know they are of a different length, but from what surface do you take the measurement?
Backing plate surface? Backing plate centering step surface or above the step that's on the spindle?

 

Click on post #66 of this thread. Click on the Ford Barn link. Click on post #9.

https://jalopyjournal.com/forum/posts/14529705/

 

Thank you.