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