hunt_activity_success_change_effect

hunt_activity_success_change_effect = {
	scope:activity = {
		if = {
			limit = {
				NOT = { exists = var:hunt_success_chance_event }
			}
			set_variable = { name = hunt_success_chance_event value = 0 }
		}
		change_variable = {
			name = hunt_success_chance_event
			add = hunt_activity_success_$CHANGE$_value
		}
		set_variable = {
			name = hunt_success_chance
			value = hunt_success_chance_value
		}
	}
	custom_tooltip = hunt_activity_success_$CHANGE$_tt
}

As written in game/common/scripted_effects/00_hunt_effects.txt.