A display apparatus, said apparatus comprising: a) a display; b) a first visual representation displayed on said display, wherein said first visual representation is based on a first data set in a measurement data record; c) a second visual representation displayed on said display, wherein said second visual representation is based on a second data set in said measurement data record; d) a first-visual-representation display marker associated with said first visual representation ; e) a second-visual-representation display marker associated with said second visual representation ; and f) a marker correlator wherein said marker correlator effectuates display of said second-visual-representation display marker in said second visual representation when said first-visual-representation display marker is placed in said first visual representation at a first location and when the data in said measurement data record corresponding to said first location is in said second data set, and wherein said marker correlator effectuates display of said first-visual-representation display marker in said first visual representation when said second-visual-representation display marker is placed in said second visual representation at a second location and when the data in said measurement data record corresponding to said second location is in said first data set; g) wherein a marker-unavailable indication is displayed in said second visual representation when the data in said first data set corresponding to said first location is not in said second data set; and h) wherein each of the first-visual-representation display marker and second-visual-representation display marker may be placed on or moved along the respective visual representation to visually identify a point of the respective visual representation, and may be used to extract a readout of the domain value and the range value represented by the marked point on the respective visual representation. a) a display; b) a first visual representation displayed on said display, wherein said first visual representation is based on a first data set in a measurement data record; c) a second visual representation displayed on said display, wherein said second visual representation is based on a second data set in said measurement data record; d) a first-visual-representation display marker associated with said first visual representation ; e) a second-visual-representation display marker associated with said second visual representation ; and f) a marker correlator wherein said marker correlator effectuates display of said second-visual-representation display marker in said second visual representation when said first-visual-representation display marker is placed in said first visual representation at a first location and when the data in said measurement data record corresponding to said first location is in said second data set, and wherein said marker correlator effectuates display of said first-visual-representation display marker in said first visual representation when said second-visual-representation display marker is placed in said second visual representation at a second location and when the data in said measurement data record corresponding to said second location is in said first data set; g) wherein a marker-unavailable indication is displayed in said second visual representation when the data in said first data set corresponding to said first location is not in said second data set; and h) wherein each of the first-visual-representation display marker and second-visual-representation display marker may be placed on or moved along the respective visual representation to visually identify a point of the respective visual representation, and may be used to extract a readout of the domain value and the range value represented by the marked point on the respective visual representation. <EOS>