8. Zero/Span Adjust.

   Adjusts the valve's zero point and span.
   
   There are two methods of adjustment:
   Angle adjustment or manual adjustment.
   With angle adjustment, the zero or span
   signal is applied, and the valve travel is
   adjusted based on the resulting angle.
   This method is recommended over
   manual adjustment.
   
   Manual adjustment involves setting the
   zero point and span point manually to
   record their position. Use this method
   when manual control is possible.