Some Gunner Zen

 I heard it was called a "make shell go straighter thingy", ... 

Cheers

Well, it sure looks like a Red Dot, but my second guess was derived from it's origin.

I figgered since our Northen neighbors politically correct government bureacratic critters are so concerned about Global Warming, that it was a 'carbon footprint' recorder. 

Judging from the blast in the picture, there's gonna be a lot of cap n' trade swapping to take care of the carbon credits used up by this gun.

Imagine the consternation caused by a Brigade shoot!  The horror, the horror!

BC - used to be, back in my father's day and my very early days, you would dedicate a gunnery trip to calibration.  I've forgotten the name of the radar system, but we had a radar chronograph that was very much like the chronographs hand-loaders use to measure bullet velocity - scaled to suit, of course,  And you went through a precise process of recording the meteorological conditions, projectile weight, propellant temps, etc, firing multiple rounds, to come up with your MVV, or muzzle velocity variation, which you used to develop a correction to your elevation to account for wear in the bore.

Then you might reorganize the platoons or even batteries to group guns by their mvvs.

Basically, that's how we *used* to answer the question.

Now, with miniturization and computers, many armies put chronographs on all their guns, and link them to the ballistic computers, which are also tracking the other variables, and the system keeps a rolling mvv by gun and computes individual corrections by gun, so you don't have to go through the grouping game.  So, if you were to find yourself in a situation where you were firing max charges and shooting a lot of rounds -  in the old days, by the end of that set of missions, you'd be shooting short - possibly short enough to notice on the ground.   With the chronographs on the guns linked to the computers - every round fired adds to the accuracy of the mvv (assuming people are doing their jobs about inputting the other data).