What is "yad soledet bo"?

Hi,

In kashrut and Shabbat, we say that food undergoes some level of cooking, and taste is absorbed, at a temperature called "yad soledet bo". Literally, this describes a temperature at which "one's hand would be scalded", such that one would pull his hand back from [unanticipated] exposure to that level of heat [Rashi Shabbat 40b]. What is this temperature, though?

Rav Moshe Feinstein tested this, and determined a lower bound of 43 degrees Celsius / 110 degrees Fahrenheit, and an upper bound of 71 degrees Celsius / 160 degrees Fahrenheit. In between is doubtful, and halachic rulings will depend on the issue involved.

(Rav Moshe Feinstein, Igrot Moshe Orach Chaim 4:74:Bishul 3)

Have a great day,
Mordechai