In a series of papers, Telting & Schrijvers (1997) have demonstrated the correlation between the phase shift across a line, ∆Ψ0 and the l-value of a mode. In addition, they found that the phase shift of the harmonic (i.e., at frequency 2ω) was an indicator of m. In this poster, we present a heuristic derivation of these results under a set of idealized assumptions. Within this framework, exact analytical formulae for the Ilrn(x) were calculated, which are available upon request.