A method, apparatus or software are disclosed for verifying a parameter value against a predetermined threshold function in which a sequence of reference values is retrieved, each reference value being associated with a respective sampling point N, said reference values representing a threshold function at said respective sampling points N; a profile type is associated with said threshold function, said profile type being arranged, when combined with said sequence of reference values, to provide an approximation to said threshold function for a region of said threshold function between said reference values; a parameter value is received for verification against said threshold function, said parameter value being associated with a discrete time P; said sequence of reference values is combined with said profile type to provide an approximation of said threshold function; and said parameter value is verified against said approximation of said threshold function.