Artillery, or "arty" for short—the SPG is a unique vehicle class that can deal some damage and stun vehicles within the shell burst radius. Shell burst causes a shell shock to a tank's Crew, which worsens a vehicle's mobility, accuracy, and reload time for a brief period.
Stun has two components:
- First component: a constant for each SPG shell that doesn't depend on the damage inflicted. In the shell settings, this value is set by a coefficient from 0 to 1, and in your Garage it is displayed as "minimum stun time" in seconds. This is one of the balance parameters of the shell—the same, for example, as penetration or velocity. This parameter is configured individually for each SPG shell, which has the ability to cause stun.
- Second component: a conditionally variable value, which is calculated depending on the damage caused by the shell. This characteristic is not specified in the game client directly, but is easy to calculate. This value depends on the damage, and is different each time.
More information HERE.