local function flightTimer(seconds) -- function to convert milliseconds to min/sec
    local seconds = tonumber(seconds)
    if seconds <= 0 then
        return "00:00";
        else
        hours = string.format("%02.f", math.floor(seconds/3600));
        mins = string.format("%02.f", math.floor(seconds/60 - (hours*60)));
        secs = string.format("%02.f", math.floor(seconds - hours*3600 - mins *60));
        return mins..":"..secs
    end
end

-- In main loop

if(timerGo == 1) then -- If switch is activated
    if(timer) then
        timeNow = system.getTimeCounter()
        timeNow = timeNow / 1000
        timeNow = timeNow - timeStart
        fTimer = flightTimer(timeNow) -- return elapsed time as mm:ss to dispplay
        else
        timer = true
        timeStart = system.getTimeCounter()
        timeStart = timeStart / 1000
    end
end