When using the artillery without the Artillery computer and without line of sight to the target (normal way of firing round far away) there is no way to know what "charge power" you have selected, you can change it by pressing "F" by default, but you can't know which one is in...
this issue makes the indirect fire with artillery impossible. it could be easily patch, with a small add to the HUD like : charge 1-2-3-etc...