How do i add to this value, instead of setting it? (slider setting)

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#1

SO my friend made a brightness slider for my game.
In the testing place, the exposure was just the normal value.
But in the ACTUAL game, its -3
So the slider doesnt properly adjust brightness, because its not the normal value.

Heres the script:

local runService = game:GetService("RunService")
local userInputService = game:GetService("UserInputService")
local lighting = game:GetService("Lighting")

local BSlider = script.Parent:WaitForChild("SettingScroll"):WaitForChild("BrightnessSlider")
local slider = BSlider:WaitForChild("Slider")

local draggingConnection = nil

slider.Position = UDim2.fromOffset((BSlider.AbsoluteSize.X / 2) - (slider.AbsoluteSize.X / 2), 0)

function dragging()
	if userInputService:IsMouseButtonPressed(Enum.UserInputType.MouseButton1) == false then
		draggingConnection:Disconnect()
	end
	local mousePosition = userInputService:GetMouseLocation()
	slider.Position = UDim2.fromOffset(math.clamp((mousePosition.X - BSlider.AbsolutePosition.X) - slider.AbsoluteSize.X / 2, 0, BSlider.AbsoluteSize.X - slider.AbsoluteSize.X), 0)
	lighting.ExposureCompensation = (((slider.AbsolutePosition.X - BSlider.AbsolutePosition.X) / (BSlider.AbsoluteSize.X - slider.AbsoluteSize.X)) - 0.5) * 2.4 --i need to add here
end

slider.MouseButton1Down:Connect(function()
	draggingConnection = runService.RenderStepped:Connect(dragging)
end)
#2

Assuming you are wanting to use the calculation as the value to add on, you should just be able to do:

lighting.ExposureCompensation += (((slider.AbsolutePosition.X - BSlider.AbsolutePosition.X) / (BSlider.AbsoluteSize.X - slider.AbsoluteSize.X)) - 0.5) * 2.4