Many of us use a non-contact thermometer with usable results, but we know that we are not measuring the bottom of our ink deposits. We have, at best, learned how to translate a surface reading to a relative temperature of the whole layer.
What the Cooper-Atkins Donut does is allow the "cross hairs" to actually be buried at the bottom of the layer of a sample print, and give a truly accurate reading of what has happened to the whole ink layer.