Thx..., an excellent article! I find myself wishing for that sort of diagnostic help a lot.

So if I understand it, per the article, the PID is an algorithmic function of the firmware..., and mentions it as a tuneable (in Marlin anyway). This is what I was trying to get at when I was speaking of tweaking heat cycling/hysteresis. In which case, the youtube vid that Chadd shared, would suggest that that the table expansion/contraction effects (if they're present in a particular machine) could be significantly improved with firmware tuning alone..., no hardware changes.

The article also mentions testing with PLA and blue tape as a means of isolating the problem, i.e., determining if a problem exists sans heating effects.

Quote Originally Posted by super fly View Post
PID=Proportional Intregal Derivative
It's a feedback controller based on current change, future change, and past change. Each term is weighted to come up with an output (this is where PID tuning comes into play). I use one to controller my smoker temperature.

Also, here is a pretty lengthy write up on z banding. To be honest I haven't completely read through yet as I don't have my printer yet. I saved the link just in case I needed it later.
https://www.evernote.com/shard/s211/...c268dcdd2d687e