Interestingly I noticed that using a simple 1.00 box size for GDX on a Renko chart has worked well as a simply system since Oct 2013, no losing trades, 80% cumulative gain, non-compounded.  However before this date it gets a lot more choppy, which makes sense because I hard set the Renko to a box size of 1 point, so as GDX changes price over time that would need to be adjusted.  

I also didn't try to curve fit a Renko size, that's why I simply selected 1.00 vs some odd number.  

also - YOU CANNOT use ATR because the past signals change because ATR changes as it's the average of the last 14 days, thus setting it to a hard box size of 1.00 allows all the past signals to be set

Again I'm showing this because it's interesting and may be something to keep an eye on, however Steve and I get our trade signals via normal Technical analysis - but it's still an interesting chart