The central part of the concave heating surface defines {HEAD ~ the lowest point} of the heating surface and the peripheral part of the concave heating surface defines the highest point of {TAIL ~ the heating surface} 
The central part of the concave heating surface defines { HEAD ~ the lowest point } of the heating surface and the peripheral part of the concave heating surface defines the highest point of { TAIL ~ the heating surface }
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL