A natural candidate would be improvements in the speed of algorithms which accomplish the same calculation on the same processor. Perhaps, from the human side, improvements in monitor resolution, at no added cost, would fall into the same category. On the other hand, squeezing more information onto the screen might or might not bean improvement from the user s point of view. Measurement and observation. Observation is quite open-ended, and can lead wherever the skills and insights of the investigator are able to take it.
Observation is an essential step in measurement.
For example, the acceleration of a sports car is given in terms of the number of seconds it takes to reach 60 mph. The reality is more complex. Operating manuals for airplanes give several key speeds for climbing, corresponding to maximum rise versus distance, maximum rise versus time, and maximum rise versus fuel expended. At a minimum, I suggest that we approach each dimension by looking for a pair of variables, whose relation over the entire range of likely use, characterizes the performance of a library, or of a component of that library. That is, the greatest benefit comes early, and further benefit is available for those who wish to persist into regions of diminishing returns.