There appears to be a minor issue with the /statcalc command's description:
/statcalc [level] [base stat] [IVs] [nature] [EVs] [modifier]
However, if you use the above setup to calc, say, Araquanid's max Speed stat, you get
Input: /statcalc 100 42 31 positive 252
Result: Base 100 at level 100...