DBPhoenix produced the attached PDF to outline his method.
Note: There is no author listed in the pdf. Another ETer stated to me credit goes to DBPhonix.
DBPhoenix stuff is rooted in Wykoff, not Hershey. There are some similarities as Wykoff and Hershey are rooted in volume.
tiddlywinks, thanks for posting the SLA file.
I can see how with training and practice a person could learn to use the hand-drawn straight lines shown in the file. From my perspective the inherent subjectivity is a bit daunting though, and I don't think I'd be very good at it, so will keep using my moving averages... really enjoyed reading about the SLA approach, though.