Set isometric crosshair

Tools tab > Drawing settings group >  Grid menu > Grid to isometric, ISOPLANE

Tools tab > Drawing settings group >  Grid menu > Left isoplane

Tools tab > Drawing settings group >  Grid menu > Right isoplane

Tools tab > Drawing settings group >  Grid menu > Ttop isoplane

Set crosshair rotation to correspond an isometric grid.

The grid must be turned on and set to isometric mode.