The list of messages in the bottom bar during battles

[jivemi]

It's not really necessary to follow those messages. "Pen1 Arm4 @ 18 degrees" means something like the shot penetrated 1 centimeter on that part of the tank (or other AFV) where the thickness was 4 centimeters, with a slope of 18 degrees. In that case it would not likely do any damage and the tank would survive.

At least, that's what I THINK it means, since I don't pay much attention to those messages. You can be sure that if the shot DOES penetrate the armor it has an excellent chance of destroying the target and you will see it get blown up. For "soft" infantry targets you get messages for casualties and for aircraft you get damage reports. But I usually rely on the visual effects to tell me what is happening.