Using software metrics to control firmware evolution

I have been working on HP LaserJet firmware as it has evolved for over the last ten years. During that time functionality has been reused, ported and leveraged across over two dozen laser printers ranging from personal home printers to office, network and color printers. New features continue to be added, such as new font technologies, higher resolutions, disk file systems, additional printing languages, different I/O protocols, copier features and color. During this ten years the size of the firmware has grown 10X in size. I'd like to share two things with you that I have found very important in measuring software. (1) gather metrics; and (2) use them! Either of these alone isn't very useful, although often done. I have seen cases in which people measure, but don't use the metrics or actually try to make decisions on subjective opinions without any data.