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What is the best way to define a numerical constant in Mathematica? For example, say I want g to be the approximate acceleration due to gravity on the surface of the Earth. I give it a numerical value (in m/s^2 ), tell Mathematica it's numeric, positive and a constant using Unprotect[g]; ClearAll[g] N[g] = 9.81; NumericQ[g] ^= True; Positive[g] ^= True; SetAttributes[g, Constant]; Protect[g]; Then I can use it as a symbol in symbolic calculations that will automatically evaluate to 9.81 when numerical results are called for. For example 1.0 g evaluates to 9.81 . This does not seem as well tied into Mathematica as built in numerical constants. For example Pi > 0 will evaluate to True , but g > 0 will not. (I could add g > 0 to the global $Assumptions but even then I need a call to Simplify for it to take effect.) Also, Positive[g] returns True , but Positive[g^2] does not evaluate - compare this with the equivalent statements using Pi . So my question is, what else should I do to define a numerical constant? What other attributes/properties can be set? Is there an easier way to go about this? Etc...

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