Charles,

Great suggestions and my compliments to a 'procedural coder' pursuing 'set-based' material!

I think it's important to note that the constants not only provided a pre-calculated constant as you indicated but, taking it further, it also eliminated the recalculation efforts with each function call. It's really cool that the ability exists to define these constants with SQL CLR.

I think I can say quite confidently that the majority of performance improvement between the various flavors of the SQL CLR functions tested was due to implicit data type conversion avoidance. (Note the performance difference between DistanceNoGlobalConsts and DistanceGlobalConsts.) That said, both aspects obviously helped to make the function faster.