I tried to make the tracker stay on track on average in sensor mode with self adjusting routines. This worked to some degree, but I am not sure how stable these routines would be on arbitrary trackers. So I decide not to make these attempts public. 

I believe it is more helpfull for the average user to find the correct settings to achieve small and stable steps in elevation and azimuth direction by adjusting the motor parameters. Then the user can adjust the trigger levels such that the tracker reacts early enough and moves in front of the sun by half of a step. 

There is only one problem. In the morning position an azimuth tracking step has a maximum effect on the azimuth sensor readings. In the zenith position, there is no effect at all. In other words, the effect on the sensor is depreciated with cos(elevation). Very well, I multiplied the same depreciation factor to the trigger level and I am presently testing the result.

In elevation, we don't have this issue. However, elevation comes to a halt at solar noon and then reverses. Considering the direction hysteresis in sensor tracking, this may lead to a long time with bad tracking, until the elevation sensor reading is negative enough to trigger a first down step. To give an example, with my present settings a reverse step requires a sensor reading which is 4 times as high as a same direction step.

This behavior suppresses forward backward oscillations but it is unwelcome if a direction reverses indeed.

Presently I am testing a timeout counter which lowers the "reverse direction" trigger level to the "same direction" level after 5 minutes without a step.

I believe these minor adjustements should work much more reliable than the self adjustment schemes I tried this week with mixed results. The former also require much less program space (still at 81% on ATMEGA328). 

Keep it stupidly simple.

If you want to have the latest version with the improvements above, contact me. For the time being I believe the changes don't justify a new release yet.

P.S. If this project should be adapted by a major manufacturer of CPV systems, I would suggest to vary the motor parameters for the Azimuth steps such that the tracker makes bigger steps at noon-time. However, this adjustment would depend on the hardware and I want to keep this solution universal.