Figure 1.

Examples of various parallelity targets, θ₀ = 0. Heavy line with no markers: f(θ) = 1 − cosθ, equation (4). Line with filled triangles: f(θ) = 1 − cos2θ, equation (8). Line with open triangles: f(θ) = 1 − cos4θ for θ ≤ π/4, equation (9). Lines with black (Ω = 1) and open (Ω = 2) circles: f(θ) = Ω²{1 − exp[(cosθ − 1)/Ω²]}, equation (7). Line with filled squares: f(θ) = (1 − cosθ)⁴, equation (10). Line with asterisks: f(θ), slack function, equation (11).