You always have a nan error in FreeTrack 2.1.2 ?
Try to change model size (in your real model) and model dimensions on freetrack software !
If you used a "3 dots cap" model you must use this kind of dimensions to prevent NAN error :
105
40 - 40
I have had this problem with FreeTrack 2.1 ...( I use 70 - 70 - 85 Hauteur - 105 de recul - Sorry for English - French language
in real and software - )
If you use "1 point" you will never had a NaN error ! (But 2 dof only - Sorry)
When you go away for your screen you must use a freetrack pause to prevent crash ....
It's a know software bug about in French "point de pivot - erreur de division par 0 - " ... If you want more information, only developpers can explain you
...
This bug has been solved in beta test of FreeTrack 2.2 ... But many others features are not ready yet ...