One rotary axis moves the head; the other moves the table. This is the case for lathes with a B-axis head.
Azimuth Angle - defines the angular limits of the machine tool in the XY plane. 0 is along the X axis; 90 is along the Y axis. Can range from 0 to 360.
Elevation Angle - defines the angular limits of the machine tool above the XY plane. 0 is in the XY Plane; 90 is along the Z axis, -90 is along the -Z axis. Can range from -90 to 90.
That is, the elevation angle limits the angle in the XZ plane. Angle 0 is the X tool, 90 is the Z tool, so a minimum elevation 0 to max elevation 90 cuts the complete right half of a sphere (flowline) given no min_azimuth/max_azimuth. (Think of it as latitudes and longitudes that are reachable. The longitude (circles parallel to XZ plane for turnmill) is controlled by elevation angles).
The latitude (think of a tool axis in the XY plane for turnmill) is controlled by azimuth angles. That is, -90 to 90 would cut the entire top half of a sphere if given no elevation limits... (X axis is 0 azimuth angle). However, the allowable range is 0 to 360, so setting minimum to 270 and maximum to 90 is acceptable (the limit is set going clockwise around positive Z axis from minimum to maximum).