= Origin-time and speed-ratio regression
{title2=$t_A=t_0+\Delta t/(r-1)$}
If $r=v_A/v_B$ and both phases share path length, arrival time of A is affine in the interphase delay. With unbiased independent clock errors, the intercept estimates <earthquake origin time> and slope estimates $1/(r-1)$. A common clock bias is indistinguishable from an origin-time shift; unrestricted station offsets also destroy speed-ratio <identifiability>. A statistical <regression> must state its clock-error assumptions.
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