WHich part of the forearm traces?

[DDL]

I erroneously used to think that lining up the middle finger and the cartilige runnning down the length of the forearm constituted level. Consequently, I traced the geometric plane with the center of the forearm or cartilige.

6B's photos showed the correct level wrist as show in this thread :http://www.lynnblakegolf.com/forum/viewtopic.php?t=897. SInce Homer was very specific defining every angle , line, orientation etc., I wonder if one is supposed to trace the plane line with the top of the level right wrist and thumbside of the forearm, as shown in that pic, represented by the black line under the word Level?

Thanks