We imagine a screen for viewing fringes placed at the light source (or we use a beamsplitter to send light from the source point to the screen). Given a steady light source, interference fringes will form on the screen with a fringe displacement proportional to the time differences required for the two counter-rotating beams to traverse the circuit. The phase shift is Δ Δ ϕ ϕ = 2 π π c Δ Δ t λ λ , which causes fringes to shift in proportion to A and ω ω .