I see this encoder on the internet(SRM50-HFA0). I need to know

1. what is the difference between "Sine/cosine periods per revolution" and "Number of the absolute ascertainable revolutions"
2. what are the "total number of steps"/"Integral non-linearity" and Differential non-linearity?
3. Are the "REFSIN" and "REFCOS" signals -SIN and -Cos signals?

Thank you.