Number of coincidences between spiral-arm intersection and ice-age epochs are plotted in black. Results are plotted relative to pattern-speed difference in increments of 0.001 km s ⁻¹ kpc ⁻¹, ranging from 10.1 to 13.7 km s ⁻¹ kpc ⁻¹, after Svensmark (2006) and Shaviv (2003). Included in the calculation is the 15.4 Myr cosmic-ray lag, however similar results with no greater hits are produced if this lag is omitted.