Simultaneous measurement of all, or most, of the five widely employed cosmogenic nuclides at sites with very well constrained exposure and erosion history is necessary for intercomparison and validation of production rates. These sites will be divided into:
Primary sites: A relatively limited number (~5) of sites with very secure histories, at which nearly all of the nuclides can be measured.
Verification sites: A larger number (15-20) of sites with well-established history, and a wide geographical distribution, that can be used to test the validity of the scaling and production formulations. These need not be datable by all of the possible nuclides.