Even with Jeng's definition, it is not clear whether "freezing" refers to the point at which water forms a visible surface layer of ice, the point at which the entire volume of water becomes a solid block of ice, or when the water reaches 0 °C (32 °F; 273 K). Jeng's definition suggests simple ways in which the effect might be observed, such as if a warmer temperature melts the frost on a cooling surface, thereby increasing thermal conductivity between the cooling surface and the water container. Alternatively, the Mpemba effect may not be evident in situations and under circumstances that at first seem to qualify.