how can i use string.sub to only display the main numbers of a script's local value?

i'm trying to make a physical text speedometer for my car, and i'm using string.sub to only show the main values of the speed in km/h, and i'm making it update if the main numbers are 1 digit, 2 digits or 3 digits, by using three separate string.sub's, but it doesn't properly work, because sometimes it doesnt switch properly, as the values change incorrectly, can i have any help with getting this to correctly work? any help is greatly appreciated!

this is the code

script.Parent.Values.Velocity.Changed:connect(function()
	wait()
	--local sps = script.Parent.Values.Velocity.Value.Magnitude (held as comment to save later)
	local sps = car.DriveSeat.Velocity.Magnitude
	local ips = sps * 10 --inches per second
	local mph = ips * 0.568182 -- miles per hour
	local kmh = mph * 1.60934 --kilometers per hour
	
	local stringnumber = tostring(kmh)
	local speed = string.sub(stringnumber, 0, 1)
	local speed2 = string.sub(stringnumber, 0, 2)
	local speed3 = string.sub(stringnumber, 0, 3)
	local spddis = car.Body.Speed.Gui
	
	script.kmh.Value = kmh/10
	spddis.One.Text = speed
	
	if kmh <= 1 then 
		spddis.Zero.Visible = true
	end
	if kmh <= 9 and kmh >= 1 then
		spddis.Zero.Visible = false
		spddis.One.Text = speed
	end
	if kmh <= 99 and kmh >= 10 then
		spddis.Zero.Visible = false
		spddis.One.Text = speed2
	end
	if kmh <= 1000 and kmh >= 99 then
		spddis.Zero.Visible = false
		spddis.One.Text = speed3
	end
end)