02 Check

mon = peripheral.find("monitor")
monX, monY = mon.getSize()
mon.setTextScale(1)

if mon.isColor() then
  colorPos = colors.green
  colorNeg = colors.red
else
  colorPos = colors.white
  colorNeg = colors.white
end

SENSORDIR = "back"

while true do
  mon.setBackgroundColor(colors.black)
  mon.clear()

  o2pos = redstone.getInput(SENSORDIR)

  function get02()
    if o2pos then
      text = "%POS%"
      mon.setBackgroundColor(colorPos)
      redstone.setOutput("bottom", true)
    else
      text = "*NEG*"
      mon.setBackgroundColor(colorNeg)
      redstone.setOutput("bottom", false)
    end
  end

  get02()

  posX = math.ceil((monX / 2) - (#text / 2)) + 1
  posY = monY / 2 + 1

  mon.setBackgroundColor(colors.blue)
  mon.setCursorPos(monX / 2, monY / 2 - 1)
  mon.write("02:")

  get02()

  mon.setCursorPos(posX, posY)
  mon.write(text)

  time = os.startTimer(2)
  event = os.pullEvent()
end