Centroid position in keV (upper panel) as determined by the Gaussian line fit, line width (middle panel), and red-shift factor of the O VIII Ly-α line identified in the high-resolution spectra of 4U1700+24 as a function of the observation time (defined as the average time of each exposure) in modified Julian date. In each panel, the dot-dashed line represents a fit with a constant, while the dashed line accounts for any linear trend possibly associated with the data (see text for details).