Left panel: frequency differences as a function of frequency of the common low-degree (1 ⩽ l ⩽ 3), low-frequency p-modes observed in spatially resolved GONG and MDI data using the m-averaged spectrum technique and in two Sun-as-a-star, full-disk observations, GOLF and BiSON, over comparable periods of time. The GOLF data were analyzed by two independent peak-fitting algorithms (R. A. García, filled symbols; P. Boumier, crosses). The comparison with BiSON is illustrated with the open symbols. The frequency differences were normalized by the combined errors. Right panel: same as in the left panel, but for the splitting coefficient a ₁.