Did you know that when you adjust the power level of a microwave oven you are actually adjusting the amount of time that the oven is cooking rather than the actual power ? The power output cannot be adjusted. This is achieved by a simple reduction in the actual cooking time in relation to the cooking time selected by the user. For instance. 100% power means that the oven is cooking all the time it is running. If 50% power is chosen, the oven will switch on and off during the cook time so that the total time it was actually cooking was only 50% of the cooking time selected. The same applied for all powers.
Power level selector
It has always been accepted between the manufacturers that to defrost frozen food in a microwave the optimum results will be achieved at 30% power. To that end the defrost setting is usually 30%. Most ovens have a range of settings that are loosely based around this. High = 100%, Medium high = 75%, Medium = 50%, Medium low = 30% and Low or simmer = 10%.