I would suggest that you have a pod_quantity for defining the various constants so that they can be safely used during the dynamic initilization phase.
I'm not sure I follow you here...could you elucidate a little more? At this point, I'm not sure whether the constants are appropriate for inclusion in the library or as an example - what I would prefer to do is to encapsulate them in something like the measurement class so that the errors are also accessible, but I'm worried that trying to include such a class would start to get out of the scope of the core library itself. In particular, I think that a measurement-like class that does standard propagation of errors would also be critical for any Boost numerical methods library (GSL provides a result type that encapsulates value/error pairs) and could share an implementation... Matthias ---------------------------------------------------------------- Matthias Schabel, Ph.D. Assistant Professor, Department of Radiology Utah Center for Advanced Imaging Research 729 Arapeen Drive Salt Lake City, UT 84108 801-587-9413 (work) 801-585-3592 (fax) 801-706-5760 (cell) 801-484-0811 (home) matthias dot schabel at hsc dot utah dot edu ----------------------------------------------------------------