Historians and economists have long been in need of index numbers to measure both the volume (real value) of activity that is undertaken to produce process or product innovations over time, and also a counterpart index that might capture the outcome of that activity (the volume of inventions) that come on stream year after year. For purposes of measurement the first index can in principle be equated (within tolerable limits of accuracy) with the real annual expenditures on research and development as recorded (at least for recent times) in governmental, corporate, company, and other accounts. Alas, for years before 1914 national or even industry-wide research and development expenditures are very rarely recorded in a form that might allow for the construction of an index number.