+10 Combat Strength vs. naval units.

As artillery became more powerful, and able to hit targets further and further away, better and faster ways of calculating the trajectory and point of impact became necessary. The time of open sights and sticking a finger in the air were over. Thus, stadiametric rangefinders … an advance over the Roman dodecahedron rangefinder as described by Julius Caesar in 'De Bello Gallico.' In effect, the stadiametric approach used a modified telescope to calculate distances quickly, based on the principle that in similar triangles, similar sides are proportional, which comes in handy when trying to hit a distant spot – be that a wall, or a moving ship. In fact, by the mid-1800s stadiametric rangefinders were found in every coastal fortification.