WD 2047+372. Top panel: chi-squared spectrum sine wave fits to all ESPaDOnS ⟨ B_z ⟩ measurements as a function of frequency of field variation. Mid panel: variation of ⟨ B_z ⟩ as a function of phase through Eq. (5), with the origin of phase at ⟨ B_z ⟩ maximum (positive) ⟨ B_z ⟩. The very precise measurement at phase 0.74 (green point) is the first ⟨ B_z ⟩ value measured using ISIS. The four data points with blue filled diamonds are the MSS data. The smooth curve is the best sine wave fit to the ESPaDOnS ⟨ B_z ⟩ measurements found from the chi-squared period search. Bottom panel: m_V-band flux variations using the same ephemeris as above.