This is a work-related question. A warm steel torus of a given diameter & thickness is left in a room held at a controlled temperature, how long does it take to reach equilibrium? Assume the air is circulating so that the torus doesn't create a warm spot. Of course it never quite gets there but this is a practical problem so almost is fine.
For example, the torus is 250mm diameter and 50mm thick (so that it has a 150mm hole). When taken from processing it is 22°C and the room is 20°C, how long to reach 20.01°C? It is resting on a measuring instrument supported by 2 steel dowels so assume it is just in mid-air.
(Such small differences in temperature are important here because we are taking very close measurements. For something this size each 1°C changes the diameter of the hole about 0.0007 mm which to us is a big deal.