Our study discovered that the Instanta gauge is not reliable because it is printed on plastic that is not dimensionally stable. Cold flow of the plastic, as it is called by engineers and technicians, causes the image to shrink over long periods of time. Thus an older Instanta will show a different gauge measurement than a newer one, sometimes as much as 0.1 gauge from true. New Instanta gauges seemed to read accurately, but we had no reason to believe they were any more stable than the older ones we tested.