Wheel Encoder Questions

I have a few questions about wheel encoders on ArduRover:

  1. When reviewing a dataflash log under WENC I see Qual0 and Qual1 values. What do these values represent?

  2. Is there a way to check the travel distance as reported by the wheel encoders versus an RTK GNSS reported travel distance?

  3. What does the EK3_WENC_VERR parameter mean? How do I choose this number, or what circumstances should make me want to change this number?