The chemical shifts and coupling constant of a spin system can generally be estimated from the spectrum when Δν /J is greater than 10. These are called first-order spin systems, with weakly coupled nuclei. As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The inner line intensities increase at the cost of those of the outer lines, as the signals are slanted or roofed towards each other. When the signals are closer together, and Δν/J is less than 10, the spins are said to be strongly coupled, and the spectra show second-order effects. Peaks may overlap completely and appear like first-order spectra, or result in shoulders and multiplets that cannot be explained simply. Accordingly, computer simulation methods are often used to identify chemical shifts and coupling constants.