In this case, marginal revenue is calculated for an infinitesimal change in output that occurs at a given level of output.Thus, Column 5 shows marginal revenue calculated precisely at a given level of output compared with the Column 4 calculations of marginal revenue between different
levels of output. You will notice that the values in Columns 4 and 5 are very similar. The differences between Columns 4 and 5 are similar to the differences between the arc and point price elasticities of demand we discussed earlier in the chapter. Remember that these are differences in the calculation of the numbers, not in the definition of the concepts