A good example is the Dimensional Analysis (DA) or Unit Conversion. In order to do the conversions, you need the definitions. To change from grams to kilograms, you need to know the definition that 1 kg = 1000 g. (See Chemtutor Units and Measures, http:/// , for the definitions you need to know and Chemtutor Numbers and Math Operations, http:/// , for the conversion techniques.) Instead of reviewing material as you would for other material, you should learn the idea and then practice the math for short times spread out far in advance of when you need it.