I have found the LM-1 to be very repeatable. I tend to recalibrate it frequently. When tuning my programable EFI, I eliminated all the peaks and dips by adjusting fuel values. When the LM-1 shows a dip, it's really there, and it will show up again at the same place most every time unless you correct for it. That's the advantage of a LM-1, you will never see the dips/peaks on the meter, you need the data log to "slow" things down to see it.
Of course, I was never really sure if a 12.0 on the LM-1 was really a 12.0. I backed some of my tuning up with a pyrometer just to be safe.