Tank Monitor

tank                    = peripheral.wrap('back')
mon                     = peripheral.wrap('front')
warning                 = 40
warnPause               = 1
pauseTime               = 2

local function centerText(text)
  x,y = mon.getSize()
  x1,y1 = mon.getCursorPos()
  mon.setCursorPos((math.floor(x/2) - (math.floor(#text/2))), y1)
  mon.write(text)
end

while true do

    mon.clear()

    amount   = tank.getTankInfo('back')[1].amount
    capacity = tank.getTankInfo('back')[1].capacity

    if amount == nil then
        amount = 0
        percent = 0
    else
        percent = math.floor(((100 * amount / capacity) * 100) / 100)
    end

    if amount < percent then
        mon.setBackgroundColor(colors.red)
        mon.clear()
        mon.setCursorPos(1,3)
        centerText("Alert")
        pauseTime = warnPause
        sleep(pauseTime)
        mon.setBackgroundColor(colors.black)
        mon.clear()
    end

    mon.setCursorPos(1,1)
    mon.write("Capacity: "..capacity.." mB")
    mon.setCursorPos(1,2)
    mon.write("Current:  "..amount.." mB")
    mon.setCursorPos(1,3)
    mon.write("          "..percent.."%")

    sleep(pauseTime)
end