I know it has been explained here in some thread that is, as it seems logical, the diference between last's day tick (Close) and the day's first tick (Open). So if Open > last Close then the Open is an uptick an you can sell short at Open. But searching the web I have also found another version saying that the Open tick sign is the same as the last Close tick sign, so the Open tick sign is determined by the diference between the 2 last ticks of the previous day. Can somebody confirm one of this two versions please? Thanks.