Most ovens take 10-15 minutes to reach the correct temperature and should therefore be heated in advance. Precision is important, so check the temperature of the oven with a thermometer beforehand. Position the shelf so that the cake will fit in the center of the oven or slightly lower. Deep cakes should be placed lower in the oven than shallow ones. If baking more than one cake at a time, stagger the pans so that one is not directly above another. If the oven temperature is uneven, rearrange the pans when the cakes start to brown. So that the heat circulates freely, the edges of a baking sheet should never be less than 1 in/2.5 cm from the sides of the oven. Trays of cakes often need turning front to back during cooking so that they brown evenly. However, do not open the oven door until a cake is set and lightly browned.