Oficaially, it standed for " Пикирующий. Бомбардировочный, Прицел " what is translated as " a diving bomber bombsight".
Infornally, it standed for " Прицел Бийоть Пилотa один раз " - a sight hits pilot once.
Thanks guys I have done a lot of reading and searching online and geez it can be very confusing but I will spray the cockpit and I.P. neutral gray, the wheel wells and landing gear iam not sure yet as far as the engine well a couple of choices. I have started to glue some parts like the engine.
Look at the diagram. It's a quite brief attempt to explain the way of attack. Mostly it is said Sturmoviks attacked diving. But it is not true. At the 50-200m of altitude, the time for diving wasn't too long and required bombs with the delayed ignition. During the time a target ( a tank e.g... ) could change its location and it wasn't easy to strike it at all. So the main way of attcking was bombing when flying horizontally or shallow diving. These lines were for altitude of an attack at 50m,100m,200m and 300m. Flying at 50m and keeping a proper speed , a pilot was looking at the line ( the first line just for 50m ) and when a target was pointed by the line endings he started to count for a few seconds then was dropping bombs. And that's all. I hope it helps.