DCL:GRPH2:UDPACK: Contour Routines: Explanation of Subroutines
Determines the interval of the contour level set by udgcla, udgclb, and udsclv.
return_value = NumRu::DCL.rudlev(nlev)
nlev (I) Specifies which contour interval to check. (the nlevth contour interval.) rudlev (R) The value of a floating-point function that gives the contour interval.