Let's say we have a reel with very consistant densities save for one small section, perhaps an eight page issue that was spliced into the reel. This actually happens a lot with older film. Now, let's say that this spliced-in section is clearly over-exposed when compared to the rest of the reel. Taking a reading from this section will significantly alter the reel's average density, especially if the technician takes only 6 readings from the reel (the more readings, the more accurate the average). Do you under-expose the reel to accomodate for the over-exposed section, or is it better to expose for the reel and sacrifice the small section? A good duplicating technician can find a happy-medium to produce a more consistant reel of microfilm that will produce good results for both pieces of film.