I can shed some light on the esignal calcs. It uses the 1 min O,H,L,C of each series to calculate the spread. Spread open is O1-O2, spread H is H1-H2, spread L is L1-L2 and spread C is C1-C2. Because the H and L can occur at any time in the bar, the two H values and two L values used to calculate the spread H and L can be values that occurred at different times in the bar. So for instruments actively traded, the spread O and C are reasonably accurate while the H and L can be either under or overstated. I trade other spreads actively and this is one of the main reasons I also run Neoticker. It can be set to evaluate the spread at 1 sec intervals and build OHLC bars from that timeseries and thus the H and L are much more accurate. In esignal, the realtime values are correct, but a refresh of the chart can produce different numbers than that which happened realtime. Hope that helps.