Relative decrease of the retrieved planet signal when stacking the cross-correlation functions using erroneous values for P and T₀ in the ephemeris. The retrieved signal is especially sensitive to an error in the orbital period, because the data is obtained over a 15 yr timespan. The error bars indicate the known statistical errors on P and T₀ as reported by Brogi et al. (2012) and Borsa et al. (2015). We stack the data at orbital periods that are deviant from the reported period by Borsa et al. (2015) by 15, ten and five times their reported standard error, but find but find no signature of τ Boo b. Thisis done to take into account the possibility of a systematic error in the orbital period, which could have affected our analysis.